For me, sometimes I think about my wife, maybe something she doesn't like (anal?) and in my thoughts she's goin at it like a crazed beast with me, and maybe someone else, usually female, once in a blue moon a male. Sometimes it's my own wild fantasies, with a hot friend or two, or some super kinky lubed up slippery fuck-fest that would probably be illegal in a few states. Sometimes it's dirty, sometimes kinky, sometimes more traditional (but always with a weird twist). Sometimes it's with another couple. Whatever works at the time. I'll go as crazy as I need to in my own thoughts to make it happen
Because what you think and what you do are two different worlds...right? Heh...