Any sized man can last how ever long in bed, size doesn't determine that, but the rest of this is a great read!
"What I've realized recently is that in some ways the fatphobia that fat men experience is as a result of sexism. In researching this idea, I found that fat men are often perceived as feminine. I found that fat men are often perceived as possessing "looser morals" or less discipline - traits historically ascribed to women/femininity. I also found many themes that pointed to fatphobia toward men, at its roots, being about anxiety that men were becoming woman-like. So, I believe that it is sexism and the deep cultural hatred of the feminine - not the hatred of men who are fat, per se - that leads to some (possibly many) of the instances of fatphobia that men experience. "
1. Chemical Feminization
2. Fat Castration
3. "Moob" Development
See the entire article along with explanations @ Virgie Tovar's blog