Definitely Mikan. Probably Nate also, for his low D rating and because he's a high usage guard who doesn't supply a lot of 3s.
I know in the previous version of the sim some players who were widely considered poison were Karl Malone, Elgin Baylor and Elvin Hayes. Some of it seemed mysterious at the time - everyone just knew you couldn't build a championship team around any of them. Since the latest major sim patch the Mailman has become a favorite - in at least theme leagues with higher caps - because of his eFG% and because (for reasons that are beyond me) he plays 100% at SF. I think cases can be made for Elgin and Elvin as poison pills, though.
Just about anyone from the '50s qualifies (except for Bob Pettit). Also lots of ABA greats you virtually never see on WISNBA teams for one reason or another.
Throughout basketball history there are some obvious lemons - guys who played a ton of minutes, put up awful numbers and weren't considered good even back then. And there are plenty of players who were stars and even legends in their day but are basically never drafted because they don't fit into anyone's cookie cutter formula. I could give lots more examples, but don't want to influence anyone's thinking TOO much.