Well I said several authors. The novelization of No Man's Land, for instance, goes into Joker's viewpoint at several points, and shows him to be really annoyed and/or revulsed by Harley's attempts to get naughty with him. (I suppose you could say that was just Harley he felt that way about, tho.)
There's the various Timm depictions, where he's by turns exasperated by Harley's sexual overtures, annoyed or angered by them, or actually interested.
If you don't want to take the cheap way out and say "Different writers just write him different ways", you could instead see it as the Joker being so deeply psychotic that he has a different set of psychoses he loads up with at any given time. Sometimes he has the ones that make him asexual, sometimes he has the ones that make him abhor sex, sometimes he has the ones where he has to get rid of anyone that might see him vulnerable, sometimes he forgets the sexual hangups entirely for a different loadout.
Joker has a modular weapons payload of crazy, and has a different combination of insanity preprogrammed for whatever situation requires it!