Could the Flash run so fast around the world that be catches up to himself and touches his own toned butt?
Actually, yes! Well, at least he could a few continuities ago. Here we go!
In 1998, during DC One Million (Wikipedia and DC Wiki), Flash and a bunch of the rest of the Justice League were taken way, way, way into the future to celebrate them as the original Justice League. How far into the future?
DC One Million … featured a vision of the DC Universe in the 853rd century (chosen because that is the century in which, assuming they maintain a regular publishing schedule, DC Comics will first publish an issue #1,000,000 of one of their current monthly titles.
Anyway, the idea is each of them will perform feats that demonstrate their powers etc to the adoring public. (Naturally, everything goes to hell both in the past and the future but that’s a story for another day.)
Anyway, the Flash’s feat? Running so fast around a populated Mercury that he actually beats himself at a race by crossing the finishing line before the after image from his first lap.
As you can see, he did it, although it’s not pictured whether or not he took a second or two to tap himself on the rear as he passed.
Ridiculous? Nope. Just Morrison. ;)