Mostly a functional response barren of any humor:
"Kinky" is asking for something that you think your partner will say no to doing because he or she thinks it is outside their comfort zone.
Using the bukkake example, if a guy and his woman host a bukkake party every weekend, at some point is ceases to become "kinky".
http://www.youtube.com/watch?v=4fk2prKnYnI