I'm guessing, "Live Action Role Play?"
In SASS, what everyone calls "Cowboy Action" shooting, definitely this is a strong factor. They spend about as much on outfits and accouterments as they do on guns -- and that's a HUGE part of the fun! If you ever have the chance to hang out at one of their matches, do it! What a hoot!
For the rest? I don't see it. While there's a certain level of convergence in dress and gear (what works, what's cool, etc.), the only "costume" or persona that's taken on is that of a serious, squared-away shooter. Unless you're role-playing the part of being a shooting competitor... how "meta" is THAT?
I suppose there are a few informal and generally low-key competition groups that do some level of cross between re-enactment and competition -- like the NSSA, for example, but you aren't going to find that in DCM, IDPA, ICORE, USPSA, 3-Gun, and so forth.
...
I can sort of see a dialog in my mind's eye about this: Some plaid & bearded onlooker asking, "
What are you guys, playing soldier or cop or something?" With the rejoinder being a laughing scornful, "Nope, I didn't come here to shoot slow and finish LAST!"