Peanut Butter Loverboy
I Was A Sixth Grade Alien, Book 4
Written by Bruce Coville
from the back cover
Pleskits quest to sample all things earthling, especially earthling foods-inevitably leads him to ....peanut butter. He adores it. There's only one problem: he has an allergic reaction to the stuff that ends up making him feel incredibly romantic. Before long, the purple alien is chasing girls around the playground, trying to kiss them. He gets a slap in the face, which snaps him back to reality. But the damage has been done, the school is in an up-roar, and unless Tim and Pleskit find a way to convince Principal Grand that it's not really Pleskits fault, the world's first alien student might be looking for a new classroom- on a new planet!