A shortenened form of the phrase "fuckin pisses me off". Usually said when the user is so pissed that they forget to say the wordpisses which adds to the vulgarity of the phrase which in turn, emphasizes the anger of the user.
Passenger:Hey that guy in the yugo just cut you off and now he is giving you the finger.
Driver:That reallyfucks me off. Hand me my gun.
Joe:Dude that sucks that your new car just got keyed.
Steve: Yeah that reallyfucks me off.