The act of winning a Party Hat in a duel in Runescape. To scalp someone, you "bet" your Party Hat and they bet theirs. If you win, you scalped you opponent. If they win, you got scalped. This term is also used for Santa Hats and H'Ween Masks.
Dude, I totaly scalped that losers Party Hat last night. I owned him, he was super pissed.