Lumpy is like a guardian to the Happy Tree Friends, as he is one of the main adult characters on the show and holds the most professions. It is thus safe to say that he knows a lot of the characters. There have been episodes that have made Lumpy out as selfish, such as Wingin' It, where he takes all the parachutes. But overall, Lumpy is a well-liked character. However, his stupidity often gets in his and others' way.
- Main article: Cuddles-Lumpy Relationship
Lumpy is shown to be a good friend of Cuddles. He has brought Cuddles, Giggles, and Toothy to play in the park, as seen in Spin Fun Knowin' Ya and Blast from the Past. In Hear Today, Gone Tomorrow, he plays with Cuddles and even wants to celebrate his birthday, baking a carrot cake for him. Lumpy is even subscribed to him on YouTube in YouTube 101: Subscriptions.
They do have a few negative interactions. Giant Lumpy killed Cuddles in Dunce Upon a Time. In The Carpal Tunnel of Love, Lumpy is clearly shocked and upset with Cuddles for putting his arm around him.
- Main article: Giggles-Lumpy Relationship
Lumpy and Giggles are great friends that sometimes have quarrels. In I've Got You Under My Skin, Lumpy and Sniffles save Giggles' life and heal her. In Every Litter Bit Hurts, however, Giggles is angry with Lumpy for continously harming the environment. Lumpy has even risked his life to save Giggles on several occasions like The Wrong Side of the Tracks, See You Later, Elevator, and Blood Donor.
Lumpy and Toothy are seen as friends most of the time, but they still do have problems. In Strain Kringle, Toothy throws a snowball at Lumpy, causing him to throw a rock. In We're Scrooged!, Lumpy kills Toothy for his body parts.
Lumpy has been shown to be friends with Petunia. In You're Bakin' Me Crazy, he attends her birthday party and even bakes her cake. Lumpy attempts to save her from a snake in From A to Zoo. In Wishy Washy, he does her plumbing. He also makes a movie with her in YouTube Copyright School and they later perform the movie live.
- Main article: Lumpy-Handy Relationship
Lumpy might be friends with Nutty. Nutty is one of Lumpy's scouts in Take a Hike and Lumpy even attempts to rescue his dead body. Lumpy makes another failed attempt to save Nutty in All Work and No Play. The two are seen playing together in Milk Pong. Lumpy grants Nutty's wish as a genie in As You Wish.
Nutty is the first zombified character that Lumpy encounters in Remains to be Seen and buries him under a ton of dirt. He is also a patient of Lumpy's in Chew Said a Mouthful, but Lumpy gets angry when he kidnaps one of his Toothy.
- Main article: Sniffles-Lumpy Relationship
Sniffles and Lumpy can vary between like and hate in the series. While they can be friends at some points, there are times in which the two share a conflict, mostly due to their opposite IQ scores.
Lumpy and Pop at first had a very neutral relationship until A Vicious Cycle, where Lumpy and Disco Bear enjoy snacks and TV at Pop's house.
In Stealing the Spotlight, Lumpy is shown to envy Pop and Cub as they decorate their home, prompting him to do the same to his home as a challenge. In Doggone It, Lumpy helps with getting Whistle out of Pop's house. In As You Wish, Lumpy grants Pop's wish incorrectly and sets Cub on fire. In Read 'em and Weep, Lumpy helps Pop with The Demon inside Cub and even sticks around to mourn Cub's death with Pop. In Spare Tire, Lumpy throws away Pop's lit match.
Lumpy does not interact with Cub very often. However, in Kringle Feast, both characters were going to eat dinner together and in Read 'em and Weep, he frees Cub from a demon, and is seen mourning his death.
Flaky and Lumpy are often shown to be good friends. She is included in groups Lumpy lead in From A to Zoo and Take a Hike. In the former episode, he cheers her up by making her a balloon animal and then carries her back to the bus. In the latter, he is horrified seeing Flaky's corpse as a bird nest. Lumpy also nurses Flaky back to health in Party Animal, swiping away Mime's peanuts because of her allergies. In Out of Sight, Out of Mime, which is one of the few times where Lumpy and Flaky interact as friends without Lumpy having more authority over her, they go trick-or-treating together (along with Giggles).
On an unfriendly note, Lumpy kills Flaky in Happy Trails Pt. 2: Jumping the Shark for puncturing a raft. Lumpy would later intentionally kill Flaky again in Dunce Upon a Time as a giant. Lumpy also had no problem with Lifty and Shifty using Flaky to provide snow for a play in Class Act.
- Main article: Lumpy-The Mole Relationship
Lumpy and The Mole are usually friends. The two are seen alongside each other in episodes such as A Hole Lotta Love and Concrete Solution. Lumpy also gives The Mole a seeing-eye dog in A Sight for Sore Eyes. Sometimes these interactions are not so friendly, like in Don't Yank My Chain.
Lumpy and Disco Bear do not interact much but are likely friends due to their latest interaction in A Vicious Cycle, where they are both police partners and enjoy snacks and beer at Pop's house. Though Lumpy didn't seem to have a problem with eating bloody chips out of Disco Bear's brain.
In A Change of Heart, Lumpy tries to find him a new heart, but only manages to get one from a whale.
Lumpy was however, afraid of being hit by Disco Bear's treadmill in Ipso Fatso, had his neck twisted several times by him, and is killed by him.
- Main article: Lumpy-Russell Relationship
Lumpy and Russell are shown to be good friends on a number of occasions. In Get Whale Soon, Russell and Lumpy try working together to escape the whale's belly. In Sea What I Found, they are both content with finding and sharing sunken treasure. They both enjoy a trip together in Snow Place to Go and they are both in a band in In a Jam. Lumpy even tried to save Russell in You're Kraken Me Up.
Their only negative interaction is in YouTube Copyright School, when Lumpy gets frustrated with seeing that Russell used his content in his own YouTube video.
- Main article: Lumpy-Lifty-Shifty Relationship
These are some of the few characters that Lumpy dislikes, as is shown in episodes like Meat Me for Lunch, Milkin' It, and Junk in the Trunk. He may still care about them though, as is seen in The Wrong Side of the Tracks, Doggone It, and Happy Trails Pt. 2: Jumping the Shark.
Mime and Lumpy do not interact frequently, but when they do Lumpy usually shows hostility to Mime. They are shown to be friends in Home Is Where the Hurt Is, as Lumpy is being entertained with Mime's tricks. However, they are not on such good terms in Mime to Five, where Lumpy makes Mime clean elephant droppings after being unimpressed by his circus tricks. In Happy Trails Pt. 1, Lumpy yells at Mime while he's choking and in Party Animal, he swipes away Mime's peanuts. Lumpy, as a giant, kept Mime as a prisoner and ends up stepping on him in Dunce Upon a Time.
Lumpy and Cro-Marmot do not seem to be very fond of each other. Their main interaction is in Wipe Out!, where they are rivals in the surfing competition. Lumpy mocks Cro-Marmot for most of the episode whilst showing off his surfing skills.
Lumpy bought some meat from him in A Change of Heart. In In a Jam, Lumpy is impressed with Cro-Marmot's guitaring skills and Cro-Marmot seems to get paid a large amount of money by him in Mime to Five.
- Main article: Lumpy-Flippy Relationship
Lumpy and Flippy's relationship can be considered neutral. Lumpy sees him as a friend, as is shown in By The Seat Of Your Pants. But like all characters, Lumpy is terrified of Flippy's evil side and will not hesitate to kill him if the chance comes by.
Lumpy seems to like Splendid, though they do not interact often. In It's a Snap, Splendid rescues Lumpy and Lumpy is very grateful for it, even at the cost of his arm. Lumpy is grateful for being saved again later in Breaking Wind when he's picked up by a tornado. In See What Develops, Lumpy sends Splendid out with The Mole to get an interesting story for the newspaper. In Just Be Claus, Lumpy entrusts Splendid to deliver the rest of the presents before he dies.
- Main article: Lumpy-Lammy Relationship
Lammy is another character that is not regularly on good terms with Lumpy. In A Bit of a Pickle, Lammy tries to explain Flaky's death, but Lumpy tazes her in the eye. Lumpy later kills her intentionally in All In Vein, along with her friends. He does seem to care about her in All Work and No Play, though he does very little to help with her very serious injury.
The closest thing to an interaction Lumpy has had with Mr. Pickels so far occurred in All In Vein, where he kidnapped and ate him off-screen.