on someone's ass

• on someone's butt

on someone's ass

1. (Canada, US, colloquial, vulgar) Rapidly chasing or pursuing someone.

   Help! The cops are on my ass!

   • 1987, Samantha Harte, Vanity Blade, Toronto, Ont., New York, N.Y.: PaperJacks Ltd., →ISBN, page 243:

     Then they saw him, his legs pumping, his face a mask of determination. "Go!" he shouted in a high voice. "They're on my ass!"

2. (Canada, US, colloquial, vulgar) Persistently urging someone on and putting pressure on them.

   My mom's always on my ass about keeping my grades up.

   • 2011, Harry Carson, Captain for Life: My Story as a Hall of Fame Linebacker, New York, N.Y.: St. Martin's Press, →ISBN, page 44:

     They would see to it that I graduated, not by pulling strings as might have been done at other schools, but by staying on my ass just as a parent would to help me off the field as well as on the field.

   • 2012, Mark Anthony Rolo, My Mother Is Now Earth, St. Paul, M.N.: Borealis Books, →ISBN, page 121:

     I slept on his couch for a few days, then he started getting on my ass about looking for work. I said, 'For Christ's sake, Frankie, I just graduated. Can I just enjoy the moment?'

• The term is usually considered disrespectful and contemptuous in formal settings, but is often used positively in informal settings.

• “be on someone's ass”, in Cambridge English Dictionary, Cambridge, Cambridgeshire: Cambridge University Press, 1999–present.
• “on one’s ass”, in Merriam-Webster Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.