The term can refer to multiple circumstances but for the purpose of this definition we will limit to white knights who frequent adult venues like strip clubs.
In the adult world, a "White Knight" is a guy who goes to an adult venue taking full advantage of the woman's perceived depravity while he is in fact being taken advantage of for his money by a girl who knows all too well what she is doing and likely rather enjoys her job, especially with suckers like these. However because he believes he is taking advantage of a woman in need, he tries to rescue her from the deviant nature of the other men in the bar and be like a respectful boyfriend.
In the end, the White Knight Syndrome sufferer constantly flames and otherwise insults the men who go there for the intended reason who have the common sense to realize what it is the girls actually go to work for each time. This makes him sleep better at night after he is a patron at one of these clubs, because he saved the girl and treated her like a true lady even if her intention was to entice deviance from the men of the club.
Also known as brown nosing, kissing ass, and being a sell out.
"So you're there to get a charge out of imposing on them to compromise their dignity more than they probably already feel they are by being there in the first place?" - White Knight Syndrome sufferer