Rosie O'Donnell could be an easy pick on HS because if she didn't know the answer, she made it PAINFULLY obvious that you should disagree with her, and that's not really how the game works.
Robert Morse was on MG in the early 70s. One of the questions was about "King Kong going _____". The contestant had a little difficulty deciding an answer and Robert is acting like an ape! Needless to say they brought back the losing contestant, not only because of Robert's dead giveaway, but because the panel alternated between APE and BANANAS, and Ira called it a NO MATCH, even though in that context, they are synonymous.
On Celebrity Hot Potato, Arte Johnson and Jan Murray didn't always play fair. When Arte was playing a question where he knew an answer, he was kinda fun to watch, but give him a question he doesn't know, and he looks frustrated. On the final show, Arte was asked to name a character in the comic strip Dennis the Menace. Instead of passing the Hot Potato and hoping the opponent didn't know,(which could've given the civilian contestant a better chance of winning), he instead gives a nonsensical answer and is out of the round. Jan Murray was equally guilty of doing the same thing. If he didn't know an answer, he'd just blurt out something nonsensical, leaving the civilian player to fend for himself.