Ive had a similar scenario - except I was sitting down the back, between the two toilets on an f100, and with them locked, a large hairy man cocked his arm ready to hit me if i didnt let him in, his other huge hand was around my upper chest, pushing me into my jump seat, after my several requests to sit down as we were about to land.
We were on long finals, in moderate turbulence.
Unfortunately the two crew up the front didnt notice the guy, as they were chattering away!!
I unlocked the toilets with my fingernail almost ripping it off and let him in.
I called the CM, who called the captain. This was in our no contact zone, as the landing gear had just lowered. Wrong as this may be, our airline had an understanding with the pilots to press the call button once, and workload permitting, theyll get to us - but only if its a fire/cabin secure issue.
The captain smoothly levelled off, slowly applied power and went around. This i suppose was helped by the fact that the airport wasnt exactly a busy one, and it was about 2300local.
The captain made a PA, along the lines of 'Ladies and Gentlemen, the captain speaking. You may have noticed us going back up - unfortunately a gentleman has risked yours and my safety by leaving his seat to use the toilet. It is not safe nor legal for me to land this aircraft unless everyone is safely restrained, so we will be up here a bit longer until the gentleman returns to his seat. We know you want to get home, however your safety is more important. Thank you.
The guy emerged, apologetic but still angry, and I sat him alone in the last row in the only available spare seat.
After we landed, I told him what he did was completely unacceptable. I reported him to operations, who in turn advised his company who had chartered about 50% of the seats on the service.
He never flew again.