A "Family Tubby" is something you give and/or receive from a
family member in a bathtub. Giving a "family tubby" primely composes of bathing and caressing a younger
family member (mainly a sibling) in a bathtub without remorse or regret
after the fact.
"Diego,
did you really touch
your sister inappropriately
when you were bathing her, she's only 5!"
"Well, yes, I did, but it was only a Family Tubby!"