- Maggie Pesky: In "Love Stinks", Melvin thought Maggie was in love with him, because she defended him against some bullies. Later, Melvin wanted to go on a date with Maggie at the Stickyfeet Swamp Club. Maggie just wanted to be friends, but Melvin thought they were a couple. Maggie later told him she wasn't his girlfriend.
- Gym Shorts Kid: Melvin and Gym Shorts Kid has a friendly relationship, as seen in "The Usual Insects".
- "Love Stinks" (first appearance)
- "The Usual Insects"
- "Best Best Friends"
- "Club Hopping" (cameo)
- "Roach Hotel"