When seated next to people of size, what is the etiquette?

There comes a moment when you are walking down the aisle of a plane and you glance ahead to the place where your seat most likely is and you think: “No, please God. Let that not be my neighbour.” And you get to the correct row and it is.

I was travelling alone and had decided to sit next to the window, thinking it would be peaceful. In the middle seat was a truly enormous 20-something bloke sporting a long red beard. When I indicated nervously that the place next to him was mine, Viking Fatty gave a gale-force sigh and said: “I KNEW IT!”

Clearly, VF was hoping that the seat would remain vacant, possibly because half of him was already occupying it. Squeezing past knees the size of bolsters, I managed to corkscrew myself into the waste paper basket of space left. My head pressing up against the window, my back twisted and VF leaning against me like a felled oak tree. It was intolerable. No way could I spend the next four hours in that position.

Politely, I asked VF if he would mind moving a bit so he was in his allocated seat, not touching me, and I could sit up straight. “The armrest’s mine,” he said truculently. VF knew his 20-stone girth was the problem. But, as is the way in these days of victimhood, he decided to get his grievance in first.

Failing to attract the attention of a crew member, I managed to wriggle a hand free and texted Himself. “Safely on board but squidged next to Viking Fatty. Going to be a long four hours.” Finally, a stewardess spotted I was in difficulties and came over. “I’m afraid I need to move,” I squawked. “It’s not me, it’s her,” protested my neighbour, “She called me a fat Viking!” Oh, hell. The brute had read my text.

Wanting to avoid a diplomatic incident, the stewardess did the sensible thing. With immense gratitude I collapsed into my own uninvaded space at the front. Dare I ask, what is the correct etiquette when you find yourself abutting, in every sense, what the Americans call a COS – Customer of Size?