Yes, you can play prank on your best man.
You threw a bachelor party for him, and make him breakfast in the morning. In addition, you held his wedding rings at the altar and now you are going to help to make his wedding day the most memorable, right?
At the wedding party, the best man was asked to put the garter on the bride. At the last moment, they decided that the best man should be blindfolded. While he was blindfolded, they switched the groom on the chair. The best man was told that he needed to put the garter on the bride. Not only that, he needed to have the bride’s big toe in his mouth while putting the garter on. They told him to be gentle and don’t ruin bride’s stocking…
The best man did what he was told. When the big toe was in his mouth, they took his blindfold off and he saw that the garter was on the groom’s leg.
Oh, well, what is a best man for; you don’t mind making sacrifices, right? That is why you are the “best man” and your pal is only the “groom.”