Most of the time, Lumpy and Giggles seem to be good friends. However, there are some instances when they become rivals due to their differing personalities.
For the majority of the series, Giggles acts kindly to Lumpy as she does with virtually every other character. She has worked alongside Lumpy in A Change of Heart and Chew Said a Mouthful. At the beginning of Every Litter Bit Hurts, she waves hello to Lumpy as he arrives to pick up her trash. She also went trick-or-treating with Lumpy and Flaky in Out of Sight, Out of Mime. She was also grateful of Lumpy rescuing her in See You Later, Elevator.
Though in spite of her sweet nature, she has been fed up with Lumpy at times. In the most noteworthy example, Every Litter Bit Hurts, she becomes infuriated by how insensitively Lumpy treats the environment. She seemed upset by Lumpy getting in the way of her and Cuddles' romance in The Carpal Tunnel of Love. And in Dunce Upon a Time, she had to rescue herself and other Tree Friends from being eaten by a giant Lumpy.
This friendship is almost as strong on Lumpy's side. In I've Got You Under My Skin, he and Sniffles were clearly worried about Giggles' health after finding her buried in snow. He, along with several other friends, also volunteered to help fix Giggles' house in Home Is Where the Hurt Is. He brought Giggles, Cuddles, and Toothy to the playground in two episodes, made a movie with her in YouTube Copyright School, and even risked his life to save her in The Wrong Side of the Tracks and the Still Alive Minisode.
Half the time, however, Lumpy isn't so friendly in her eyes. He angers Giggles in Every Litter Bit Hurts due to his apathy towards the environment; while he himself remains friendly in the episode, he shows no concern for his misdeeds or Giggles' complaints. He attempted to capture and eat Giggles in Dunce Upon a Time and later succeeds doing so in All In Vein. He was also somewhat harsh to Giggles in A Change of Heart, but to be fair, their patient was in critical health and it may have been due to stress.
- They, along with Toothy and Cuddles, make up the four primary characters of Happy Tree Friends.