Knock on the door a few times to make sure

I went to a place once where the lock had a red or green thing over it to indicate if it was locked, that way you don't have to worry about pushing a locked door

Fun story. I once really had to pee. It was a single person bathroom at a Dunkin' Donuts. I get in there, and the lock for the door is broken. I almost didn't want to use it but I really had to go, so I thought to myself, I'll be quick, it'll be fine. Never. It's never just fine. Well as I'm standing there peeing, this guy with a kid not only doesn't knock, but opens the door, sees me standing there (at this point I stop peeing and I'm trying to cover up my junk) and apologizes. However, instead of instantly closing the door like a normal human being that has any sense of respect for other human beings, he proceeds to walk in, as I continue to shield my junk, and walks over to the sink to grab some paper towels and then leaves. There is no excuse for this, and if you so desperately need paper towels, ask at the damned counter. Thank you!