on someone's ass

prepositional phrase3

1. •
   (informal, vulgar) Rapidly chasing or pursuing someone.

   • Help! The cops are on my ass!
2. •
   (informal, vulgar) Tailgating someone.

   • Why is this guy on my ass? I guess doing ten over the limit isn't enough speeding for this moron.
3. •
   (informal, vulgar) Persistently urging someone on and putting pressure on them.

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