I had an experience, years ago, when I was visiting Berlin for a sex holiday. I was chatting to one guy who said that he was big and wanted to be really sure I could take it before meeting up. He said he is getting sick of hook ups, as he puts in the time and effort to get ready and come over for bottoms who can never take it as he is too big. I told him I had taken 100+ cocks before without issue, so I did not think it would be a problem.
Half an hour later, I am having to turn him down after a couple of minutes of fucking. He was huge and poppers was not enough for me to relax enough and take it. I was really embarrassed as I had never failed before. In these days, I had not really discovered the more "extreme" porn or gotten into playing with big toys and I genuinely just believed I was loose enough for anyone.
I have stretched myself a lot since then and could take anyone now, but the amount of foreplay needed could vary. I prefer to do the foreplay with toys on my own anyway.