Jolly Rogering
when your standing in the shower and you rub butts with your g/f and it just feels odd and really slippery. 
she bends over for the soap and instead ramming your penis in her butt, you turn around, push your butt against hers and jolly roger the shit outta her.

Tip: hold her hips she she can't run away and rub vigorously!
Jolly Rogering is fun for anyone