2. An exclamation used to establish one's status as the alpha male, and to put down any possible challengers.
3. To physically strike a bear in the mandibular region.
The word is highly versatile and adaptable to new situations. No matter, it gets the point across.
2. Joe: Do you wanna fight?
Matt: Bitch, I Punchabearinnamouf!
Joe: Oh damn I was uh... just kidding!
And then Joe Runs away.
**Note: in some situations, one might place extra emphasis on the "bear" part of the word, just for extra authority.
3. Dave: We were camping and this bear tried to steal the fish that we just caught!
Phil: What did you do?
Dave: I Punchabearinnamouf!