'for that ass' means 'for you' (just another way of saying it). It has nothing to do with the actual body part, it just means I'm giving you something.
Originally coined by Joanlebaptiste of chaturbate fame as "Put that ass on that line". It was later modified by user _gustave to "On the line for that ass".
That girl just doesn't want to get with me. I'm on the line for that ass.
Nickname given to bales of marijuana thrown overboard or out of airplanes. Origin is reportedly from members of the US Coast Guard in the area of Southern Florida.
"Base we've got some square groupers floating outside of Miami harbor."