Go sniff your co-worker's head. If it doesn't smell like cheese, then go ahead and borrow his/her helmet.
If your head smells like cheese, that's OK.
__________________
"...in Las Vegas where -the electric bills are staggering -the decor hog wild -and the entertainment saccharine -what a golden age -what a time of right and reason -the consumer's king -and unhappiness is treason..."