He blind-sided me or took me down for no reason. The phrase is in reference to the Seinfeld episode in which Kramer buys the Commando 450 shower head to replace the low-flow shower head in his appartment.
Kid 1: (talking to girl) You know I play guitar...
Kid2: Yeah, to make up for your small genetalia!
Kid 1: (to Kid 2) Dude, you kind of 450'd me back there!