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1.
a very convincing, meatless, substitute for ground beef. Wannabeef is not often generally consumed by anyone but vegetarians &/or vegans and varies in its degree of palatability.
Person A: "Wow, this meatloaf is so delicious!"

Person B: "Actually it's meatlessloaf. I made it with wannabeef."
by sara90 December 07, 2009
 
2.
A phrase used to start a fight. Usually after someone else says some thing really offensive to you. It can also be used after someone show aggression to you. Ex. push hit.
Bill: Your mom's a bitch.
Bob: Wanna beef?
by bobmcdoogal January 20, 2012