1. To totally screw something up, specifically by doing something irrisponsible.
2. To ruin a movie, TV show or book by acting in a totally over-dramatic or camera-false manner. Happens an awful lot in American Mainstream.
1. All I was trying to do was finish my homework but you had to go and Arsefy it by drawing a massive penis across the page in indellible marker.
2. Some of the shows on TV have potential, but there is always one character who Arsefys it by talking in sound bytes.