Dear Thai Tai,
I understand that your staff probably don't want to deal with having to clean up a customer bathroom - especially since you're situated on 17 Ave. I worked a few blocks down for a year and I only let pregnant women and children use our store's bathroom.
But don't put an "Out of Order" sign on your bathroom door if your staff is going to use the "out of order" bathroom TWICE while I wait for my sub to be prepared. That's just bad form.
Minus 4 stars for lying, extra star because I USED IT ANYWAY, HAHAHA!
Protip: Lock the bathroom door and have customers request the key.