So I'm sure many of you have seen the video where some professional NBA player disguises himself as an old man and schools young people at street basketball
https://www.youtube.com/watch?v=8DnKOc6FISU
A running version of this would be pretty great. Picture Dathan Ritzenhein dressed as a grandpa, wearing jeans, flannel, the whole 9 yards. He shows up to a fairly competitive 5k which usually has a winning time around 16 minutes or so. Even with the whole get-up, he'd still dominate, and it'd be hilarious to see all the singlet/short short wearing competitors scratching their head as to why they lost by over a minute.