never interrupted when alone but my wife and I have been interrupted many times. a few are memorable. the time my wife's friend and our neighbor rang the doorbell right as my wife came and called out my name, a few seconds later in a real quiet voice we heard, "I'm sorry. I didn't know you guys were fucking. I'll come back later." about a year of so later, that same neighbor caught me napping nude after a fuck session, "you're HUGE! now I know what she sees in you." she spent the next few months trying to get my wife to agree to a threesome. that didn't happen. she did not real appeal to me anyway.
it was pretty common for me to come home after work and we would fuck daily. a male friend of mine got in the habit of dropping by without a phone call. after about 3 visits and me answering the door with a hard on, I told the guy this has to stop. and you know what, he still did it 2 more times. "dude, I'm in there laying pipe. you gotta call first." he stopped.
my wife's co-worker lost her office key and stopped by unannounced to get my wife's key. I answered the door with my gym shorts on with my massive cock ballooning the shorts outward. it was the first thing she saw, and she was speechless, stuttering, hem-hawing. finally, she explained what was going on. she later apologized to my wife, and told her I had a big dick.