I'm not going to tell a waiter I was undercharged
Why did you decide not to tell the waiter about being undercharged?
It's OK for waiters to make little money. They already have a job.
You should always be honest. They need money and you shouldn't lie about an undercharge.
I'm going to leave a shitty tip too because I do not care.
You should help people out by correcting a mistake that will cause them a big problem at their job.