CM Punk isn't undefeated at SummerSlam. In 2010, The Straight Edge Society lost to The Big Show in a 3-on-1 handicap match, and in 2011 Alberto Del Rio cashed in on Punk.
A few I can think of off the top of my head:
The Miz is undefeated at WrestleMania, apart from the WrestleMania 25 dark match that the WWE doesn't recognize.
Alberto Del Rio is undefeated at Royal Rumble (won the RR in 2011 and beat Big Show in 2013), and Elimination Chamber (beat Kofi in '11 and Show in '13).
Cena was undefeated at Survivor Series until last year. 9-1 I think his record is.
Cena is undefeated at Extreme Rules. (Beat Show in '09, Batista in '10, Miz & Morrison in '11, Lesnar in '12, and drew with Ryback in '13). 4-0-1.
Obviously MICHAEL COLE is undefeated at WrestleMania! How could you forget that? He mentions it every week!
I'm sure there are more.