I can only think of one time that a guy turned me down because I was too big (and I am not that big). My ex(boyfriend at the time) and I were hosting an orgy at our house. This guy had asked for an invitation. He sent me some pics that I were sure were fake pics, the guy was really hot and he looked like he should be a model. We chatted for a while and he told me how he went to the bookstores and bathhouses in Chicago all the time and got fucked by many guys. Even though I was sure he wouldn't show up (or he would show up and prove that the pics were fakes), I sent him the address.
The night of the orgy, he arrived and the pictures were of him. He was very hot looking. Every guy at the orgy tried to get with him but he turned most of them down. At one point, he was getting by one guy, so I took him up to a bedroom while my ex and a friend told the stalker he had to leave. While we were upstairs, the hot guy told me he really wanted me to fuck him. I told him that I would love to fuck him but not that night. I told him that if my ex agreed, he could come over for a 3way with both of us. He said he would love to do that, so we agreed for him to show up in 2 weeks.
During those 2 weeks, we chatted a few more times. He told me about how he went to Man's Country (a bathhouse in Chicago) and got fucked by 15 guys over the weekend. Told me how a couple of them were well hung. He couldn't wait for both of us to fuck him. On the night we agreed upon, he showed up and was in a great mood. All 3 of us chatted for a while and had a few drinks. We then went to the bedroom and all 3 of us got naked, made out with each other and sucked each other. Finally, my ex who loved to rim, started rimming his ass. We had agreed that my ex would get first crack at his ass since my ex was smaller than me. After my ex had loosened him up, my ex lubed up his hole really good. When my ex tried to slide his dick inside of him, the hot guy started complaining about how much it hurt. So for the next 15 minutes, my ex fingered his ass and kept applying more lube. The entire time, the hot guy complained about how it was hurting. Then the hot guy said he wanted me to fuck him. I told him if he couldn't take the ex's dick, he wouldn't be able to take mine. He insisted that he wanted me to fuck him. So I lubed up my dick and rubbed the head of my dick up and down his hole. The first time I tried to push the head of my dick inside his hole, he started crying about how much it hurt. So I tried to stick a finger in his hole but he complained about how it hurt. I was over him at that point so I told him it wasn't going to happen. He was upset that I wouldn't fuck him. I never did figure him out, but he was either lying about getting fucked by all those guys or he was lying about it hurting.