I'm not a "stunt runner" but I do like a good dress-up dash. The pressure of racing for a PR is disappears, eclipsed by the challenge of finding the perfect running costume.
I personally like a costume with a bit of irony and that doesn't chafe on the run.
A few of my DIY Halloween costume favorites over the years...
The "road runner"
(This is the ONLY time you may ever refer to me as a "jogger.")
Cookie Monster (Props: blue clothes, fuzzy knee socks on arms and legs, and a bag of Chips Ahoy)
Hooters Waitress (The costume is self-explanatory, but it's worth noting that this was the first and LAST time I'll run in pantyhose. But maybe NOT the last time I'll run while carrying a pitcher of beer.)