Pinkie Pie notices that a peppermint turned her tongue green, prompting Rarity to recite a poem about a kissing game. They both decide they want to play it. Their target: Rainbow Dash.
Rainbow Dash doesn't know about this game and treats their sudden affection like a prank. Naturally, she feels the need to prank them back, but she doesn't think her plan through and things rapidly spiral out of control.