To mess up something simple that you do right all the time. This usually occurs in a big situation, such as a test, interview or superbowl.
I had three tests last week and I would have had A's but I welkered parts of all of them.
A 13 year old siren, without the beautiful voice, but still manages to lure people to their death (usually self-inflicted).
Guy 1: Did you see that new Rebecca Black song?
Guy 2: Yeah it made my nose bleed.