Their level of "taintedness" makes it questionable as to whether or not you should be involving yourself with that person,usually, and especially in an intimate manner.
There are several factors involved with determining the degree of a person's "taintedness", such as;
-How well one knows the person or people, that the tainted individual was with (and if you know and don't like that person, then the "taint factor" is waived and becomes more of a "Yeah, I banged that asshole's ex!)
-How long ago that relationship or encounter took place,
if that person had been with the "tainter" last night, their "taintedness" would be just about radioactive...
on the other end, there is a standard five year statute of limitations and the taint in most cases has worn off.
-Some degrees of "taint" are infinate, such as Brother's ex-wife, ex's of parents etc.
-The combinations of situations and connections are so numerous that there is no exact science for taint determination and each case must be evaluated on it's own.
In most cases there should be an individual who has the experience and knowledge to act as "Judge of the Taint" to rule on tainted individuals for you or your social circle,and that person's judgement should be taken into consideration before going ahead and doing whatever you were going to do in the first place.
A guy is tainted when he has sex with a girl who is tainted.
Person 2: Damn, she's tainted.
Person 1: Mike just had sex with melanie.
Person 2: Suck for him, he's tainted now
I swear to god, if Leland rats me out one more time I'm gonna taint his mouse!