Shortened way of saying "But you know what?" Said in a fast, Wisconsinese accent.
Jim: Yesterday I thought aboot all that cheese I ate a long time ago...

Bob: Yeah?

Jim: Buttchaknowhat? Explosive diarrhea ain't all it's cracked up to be.
by Neenja! October 10, 2009
Get the Buttchaknowhat? mug.