Derivation of wtf and is an expression used to illustrate surprise and slight confusion.
History of the word comes from older Quake 1 days (1996-97) in which it became common lingo on the internet to say ombear instead of omg (thus bear replacing God for those who praise the bear). Adding Bear to words became popular and quickly afterwards, "bear" replaced the "f" in wtf and this is how "wtbear" was born.
<RandomPerson1> Hey I just saw my neighbour bring in two huge bags from his truck.
Wtbear did you do ??
Used alone, often after some surprising event: