When you talk to someone too much and go over the top to be nice to them and continue the conversation until you eventually invite that person over for a hot tub later that night.
When you stick your face in between your partner's butt cheeks, put your lips together, and blow like your making your own hot tub in the bathtub. Also known in some circles as speed boating, or motor boating the backside.
The wife thinks it tickles when I go Hot Tubbing, but I think it's fun. So long as she doesn't fart on me!