I'm amazed at the people that go long flights without ever hitting the lav. Like 12 to 15 hours. I always try to wait for my seat mates to make their trip so I don't have to disturb them, but that doesn't always work out.
On a recent 14+ hour flight to Korea I was in the window seat and around 4 hours in, after the meal service but while my seat mates were still awake I put my stuff away, folded the tray table, and said "sorry" in English and Korean while pointing and looking aft. The older lady next to me just stared blankly at me until her daughter explained to her at length that I needed to get up. She chose to just fold her legs and I had to disturb the people reclined in front of us and do the lav straddle.