My co-worker lectured me on rudeness of a large tip

[yellowcanine]

45. It is ok to ask fellow diners what might be an appropriate tip. It is not ok to lecture someone

about leaving too large a tip. In general it is best for everyone to tip as they feel appropriate and not notice what others are tipping. There are exceptions, such as one where someone buys the meal and the other diner says, "I will get the tip." and then proceeds to drop a very stingy tip on the table. In that case it is up to the other person to quietly correct the situation if they can - but correct it as graciously as possible if not. I have actually had to do this with my dear mother, who doesn't understand tipping. Now I just make sure I put an appropriate tip on the credit card slip. The only times it is inappropriate to leave an overly large tip is when the tipper is obviously trying to curry inappropriate favor (in other words a bribe) with the server or to obviously "show up" other diners. But if someone tries to discreetly leave a larger tip and someone else gets nosy the shame is on the nosy person, not the big tipper.

One general caveat on "quality of service" and tipping. Yes, very good service should be rewarded. But it is not the server's fault if the meal is improperly cooked and you said nothing about it so don't punish the server for that. For not noticing that your water glass is empty, or for not asking if you need anything else, yes, tip the minimum. (still 15% imo.)

I don't see how a larger than usual tip "degrades" the server unless it it is obviously a bribe with the implication of some kind of inappropriate reward, such as sexual services or not noticing that you stuffed the silverware into your purse.

My favorite large tip story is a friend of mine who always eats at the same restaurant on the anniversary of his brother's death and leaves a $100 tip in his memory with a note explaining the situation (it was his brother's favorite restaurant).