A relational distinction. If you sleep with a girl, then your buddy sleeps with her. You are his peter-in-law. The relationship is one way. You would not be his peter-in-law unless you sleep with that girl again *after* him.
Sean Penn (Madonna's ex-husband) is the peter-in-law of Guy Ritchie (and let's face facts, a bunch of other people too!)
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."