Can't. Stop. Laughing. If you thought you had major fangirl moments online, you're in for a surprise because your fave celebs have those moments, too! Whether it was before they were famous, like Austin Mahone's total freak out over Justin Bieber, or after they made it big, like Ariana Grande having a mini heart attack over Bruno Mars, you don't want to miss their insane reactions.
Click through the gallery, then let us know whose Twitter fangirl moment made you laugh the most in the comments below!
Click through the gallery to see your fave stars' major fangirl moments on Twitter!