There's nothing wrong with saying “No.”
Most of the time, saying "No" is the best thing you can do for your productivity, progression, and sanity.
This is something that took me a long time to understand myself.
...and had I started saying “No” earlier...
I would have spared myself a lot of time and frustration.
Learn to say "No.”
Learn to say it unapologetically.
Learn to say it often.
When you say "No,” you aren't letting anyone down or being selfish.
If anything ... you are doing these people a favor by bringing awareness to their shortcomings and giving them the opportunity to better themselves.
For that, they will be grateful.
Saying "No" to bullshit is the same thing as saying "Yes" to a more peaceful and productive life.