Knock knock

Someone's in here! Hold on! One minute! Seriously, how many times does someone have to knock on my dressing or bathroom door before I figure out the best way to respond? No matter what I say, I always feel humiliated. Tonight I was changing for Zumba and a girl knocked on the door... i said "Sorry! Ope! Um!." An apology, right into my oh+oops combo, and then enough weird sounds for her to figure out she had to use another room. What I don't understand is when people knock on stall doors. Can't you just look for some feet? When that's the case, I give a "Yup!"... or sometimes I phrase it like I think they're knocking purposefully,"Yup?" Stupid. One-stall bathrooms are bad too, you have to yell extra loud. One time I must've responded with something that wasn't quite clear, not surprisingly. But the woman actually said, "what?" ...Does it really matter? You heard me respond with something, I am not a talking toilet animal, nor are these walls able to speak, so just hold it in and wait. The worst is at work when the custodian gives a knock and asks if its clear, because you know everyone can hear your response since the door is open. I've contemplated just staying quiet, but figured him finding me in the stall would be much more painful then telling him to wait a sec. I guess I should be thankful though, Lord knows some people don't stop at a closed door. Is there ANYTHING more humiliating then getting walked in on? And there's just nothing you can say or do to recover from it either. One time, I had to pee so bad that I actually threw my head back and closed my eyes. When I woke up to the world again a few seconds later, I realized my stall door was wide open, and people had seen me sitting like that. Bathroom Fail.