smoker's remorse 

The feeling you get when you light up a cigarette, then halfway through, you realize you don't feel like smoking it anymore.

Dude, you wanna finish my cigarette? I've got a bad case of smoker's remorse.

smoker's remorse by James_DP March 11, 2009

Smoker's Remorse 

Regret of one's negative decisions that have placed them in their current situation, such as smoking leading to lung cancer, causing regret.

Tom: My mom is upset because she's gotten so fat she can't see her toes for her stomach.
Mike: That's just smoker's remorse. She shouldn't have sat on her ass so much.

Smoker's Remorse by Elroy from The Office June 18, 2020