This technique was used against me many years ago by my mother during a game of shuffleboard. I couldn’t have been more than ten or eleven. It was me and my dad versus her and my sister, and we were creaming them — mainly because of my totally unexpected deadly accuracy. Then came the point where she told me, “I noticed that when you’re lining up a shot, your eyes click back and forth along the shuffleboard court in discrete little steps, like a robot.” And that was it for my deadly accuracy. I was completely self-conscious for the rest of that and every subsequent shuffleboard game. Not necessarily because I cared how my eyes looked when I was playing, but because I began actively trying to replicate the proper eye motion that had yielded such good results. Of course it couldn’t be replicated consciously, and trying to do so only made me sure I was doing it wrong, which wrecked my confidence and hence my ability (since confidence is 90% of ability). And of course trying not to do it consciously was hopeless. (“Don’t think of a pink elephant!”)
The effect of my mom’s comment was so immediate and so apparent that she quickly apologized and has re-apologized several times over the decades. I’m willing to give her the benefit of the doubt and believe that it really was unintended. But if she really had meant to negate our team advantage and even the odds, she could not have been more surgically precise about it.