Get your ass in gear
Definition 1 of 1
Pro Tip 1/3Colloquial Tone
Used in casual or informal situations, not in formal writing or speech. 
Come on, get your ass in gear, or we'll miss the movie!
Pro Tip 2/3Urgency
Expresses a strong encouragement to act quickly or immediately. 
You better get your ass in gear, the deadline is today!
Pro Tip 3/3Slightly Rude
Can be considered impolite or aggressive, so use it with friends, not superiors. 
I told my brother to get his ass in gear with cleaning his room.