Little Albert was shown little furry animals. Like any baby, he wasn't afraid. That is, until the experimenters repeatedly scared the poop out of him every time he saw a furry animal. They'd make a loud clang with a metal bar when he saw a rat, and that would make him cry. After a while, they no longer needed make the noise; Albert had successfully associated the loud noise with little furry animals, and the animals themselves would make him cry. Even a mask of Santa Clause freaked him out. Check out this sad video.
His family moved away before they could undo the conditioning. Such an experiment would not be allowed on a baby today. Poor little guy.
If any man took a Santa mask and got THAT in-your-face with any of my kids, I'd give HIM a dose of conditioning.
According to Wikipedia, Little Albert died of hydrocephalus at the age of 5.