Very nice! I think we've all used outside inspirations during sex. I've fucked my wife quite a few times and thought of some beautiful woman that I saw earlier in the day or a nice cock that I sucked on in the past (or recently). Hell, I even thought about the time I accidentally saw my niece's sweet tits - that was a great fuck session!
I was flashed by a guy near my college and the cock was very much like this one. Big thick head. I was scared and got away from him but could not forget that cock. I later fucked my boyfriend and came twice thinking about sucking that big dirty cock.