A weak/skinny/little person
Hey! Look at that lil slimpy! He needs some meat on those bones!
to feel someone quickly under the chin in a reverse jab-like motion while saying "slimpy" and having sexual thoughts in mind.
Josh walked up to the schools super hot and popular 'Kelly' and performed the quick task of a slimpy. His friends were very impressed while Kelly had no idea what had happened. Josh remained a virgin until he was in his late 50's