a man, usually heavier built, who can handle mass quantities of alcohol and/or weed and still keep going.
Joe: "You see that bigger guy over there just slamming those beers down?"
Mitch: "Ya man, thats Bill... he's such a tankapotamas."
Jared: "Dude, Josh, you've hit that bong like 8 times!"
Josh: "Yo bro, i'm a motha fucking tankapotamas"