(1) An insane person's sexual orgy.
(2) Slang - a derogotory term describing a gathering of people deemed to be insane.
(1) "Wow man, did you hear about those 5 people from the mental assylum having group sex? I guess you shouldn't really leave those people alone in a room together. A madsome to remember!"
(2) "Hey man do you see Crazy Cath, Bonkers Bill and Schitzo Sam over there talking?"
"Yeah man, what a freaking madsome."