A male butt that is nice,big,and round. Manbutts come in all types! hairy,beefy,muscular,jiggly,soft,hard,tight,or loose... The Manbutt is mostly enjoyed by gay men who fuck it and/or toss its salad/rim it or just flip it,rub it up,and smack it,slap it, spank it ,and wank over it. Straight women may also enjoy the manbutt.. She may grab onto it and squeeze while having sex.
A general name for a guy who makes disgusting jokes about butts, assholes, shit, etc. as well as sexual acts relating to butts and or shit. Marcbutt also knows the name of obscure sexual acts. Can be used as a term of endearment if you enjoy Marcbutt's jokes and knowledge.
A chick gave me a stingbug last night when we were fucking and it reminded me of Marcbutt.