history: I knocked on a closed bathroom door and no one responded. But, when I opened the door, someone was using the bathroom.  I can't believe I walked in on someone using the restroom.  Oh my_comma_ that must've been an embarrassing situation! It was! I knocked first and no one answered_comma_ so I thought it was okay to go in. 
current: That's ok, you did the right thing. It probably happens to lots of people.
next: Thanks, I'm sure it does haha