I went to work wearing my uniform but have no underwear on.
Why didn't you wear underwear to work?
I forgot them in the house.
It's no one's business but your own what you wear under your work uniform. If you don't want to wear underwear, or forget it at home, then that's your business. I would recommend not talking to your coworkers about your choice of undergarment, though.
I can't help it if other people see it and find it funny.
You don't have to draw attention to it though. It's up to you if you wear underwear or not but keep it to yourself. No one needs to know what you do or don't wear to work.