A purposely vague euphemism
. While it usually refers to enthusiastic
sex, I think it can be used for anything that involves boinking-esque movement and is enthusiastic
Here are a few reasons:
First, there are many sexual acts that need names that are comfortable for people to say - i.e., names that sound neither rude nor stupid.
Second, gentle humor and sex go well together if everyone involved agrees - such as singing the Monty Python song Sit On My Face after engaging in the appropriate amusements.
Third, it's just fun to be deliberately vague and leave others wondering exactly what it was you did.