An annoying person who responds to hearing someone else’s experience or problem by immediately telling a similar story about themselves with a much more fantastic outcome. They've done everything you have, only more often... and better than you.
You: I got to meet Engelbert Humperdinck before the concert and I got his autograph.
Topper: Yeah, well my cousin knows his producer, and he got us front row tickets to the show and then we went backstage and met him! Then he invited us back to his hotel room and we partied with him all night.
You: Ow. I have a a dislocated knee.
Topper: Yeah, well last summer I broke my leg in four places and had to have titanium pins inserted. I also had to have surgery done on my knee to repair the torn ligaments. I was on crutches for almost two months... and I always set off the metal detectors at the airport!