Cabbies are disrespected by everyone.
But their car cannot be. It is as levelling as a gun to an abused geek. It puts them on the same ground as every other person on the road and they can feel it.
So when these guys have a bad day, have a rough client, or are just pissed off about something in general, their driving will reflect that.
I have RARELY seen a cabbie with an "Off Duty" sign, especially if their family is in the car, cut someone off, tailgate, or drive obnoxiously, so that should tell you something.
But it is a two way street. You be nice to a cabbie, it makes them nicer to you.
Oh, tip. Use cabs to get uptown or downtown. Walk crosstown to the avenue you want (and direction it is going) and graba cab from there on. You can, in most instances, cover most of manhattan in a few minutes.
As soon as you want to go crosstown, it can sometimes be slower than walking. And definitely more expensive!
Also, I am one of those people that asks for the 50 cents back at times. Why? So I can give you a tip in whole bills ya grump!!!! ;P