Think of something funny and/or misfortunate to happen to someone you dislike, then look at them and say the words"I curse you."
Examples include causing the chicken from one's meal to vanish, or reversing the direction of one's gravitational pull.
"You can't do that or I'll curse you!"
--
"I'm sorry about when you both met Asher in the parking lot, he was wrong not to give you that money."
"That's why I Tiny Cursed him!"