Man... i've had a few.
Spilled half a bottle of super thin tire glue on my shorts while wearing them. Next time you are gluing tires get a piece of cotton cloth and put a little on, admire the smoke and then imagine that stuck to your leg.
Nepalm.
Not being able to start car before a 20 minute final, changing plug, running out starter box only to realise it had no fuel in the tank.
Two rear tires coming unglued in a final costing the win, maintained second though
Wheel coming off in warm up lap for a final.
When i started i ran pure white shells on my Kyosho. One random day someone else had the same at the local track, i didn't notice in qualifying and he snuck into the back of my final without me noticing.
Yup.
Fell over marshalling a kids car in practice, slipped a ripped my trousers from knee to crutch.