Unwanted and excessive jiggling and swinging of the male genitalia during pelvic thrusting, often caused by the lack of restrictive underwear. Sometimes causes nausea or vomiting in others.
Girl #1: Did you see Johnny dancing last night? He had a seriously disgusting case of floppy junk going on.
Girl #2: Yeah, it made me want to blow donkey chunks. Jesus, buy some boxer briefs, dude.