Now "doesn't fit" really covers a lot of situations:
The person being disgustingly fat - I'd feel repulsed and run away
The person being overweight - I'd feel less attracted, but would most likely engage in some BDSM
The person being normal weight, but plain ugly - I'd feel less attracted, but would most likely engage in some BDSM - using a hood, maybe?
The person being overly skinny - I'd be scared to do something wrong and run away
The person having the same gender as I - I might engage in some BDSM, but it wouldn't be wholehearted.
The person being very young - I might engage in some BDSM, but it wouldn't be wholehearted.
The person being too young - I might engage in talking about BDSM, and might do simple ties. It would not be a sexual thing for me though
The person being old - as long as the brain permits them to consent, there's no problem about extended age
Handsomeness and beauty will stimulate my pleasure (or rather my ego). And I might be careful not to ruin a perfect body.
Etnicity really doesn't matter much to me - maybe it can be used in roleplaying/scening an encounter (whipping the nigger, tieing up the russion spy, putting the chinese in japanese bondage, having the british girl dress even naughtier than she would do herself).
So - I guess the desire to do BDSM will win most situations
TeaSer