To rile someone means to annoy or irritate them deliberately, stirring them up until they become agitated or angry. If your little brother keeps poking you while you're trying to read, he's trying to rile you up. When a bully makes fun of someone's glasses hoping for a reaction, they're trying to rile them.

The word suggests getting someone genuinely worked up, like stirring up mud at the bottom of a pond until the whole thing becomes cloudy and turbulent. A clever debater might rile their opponent on purpose, knowing that angry people make mistakes. A sports fan might get riled up watching an exciting game, shouting at the TV as the tension builds.

You'll often hear rile paired with “up”: someone gets riled up about unfair rules, or a provocative comment riles up a crowd. Animals can be riled up too. A dog might get riled up when a squirrel dashes across the yard, barking and straining at its leash.

People can recognize when someone's trying to rile them and choose to stay calm instead of giving the reaction the other person wants.