[AlethiaSi]

I am a waitress now, and have been in the industry for about ten years. I've worked in family style places to friendly's to top notch. If someone is nice to me, I'll go out of my way to help them, plain and simple. (I also send over a tasting plate, give a free dessert, etc if things aren't great, sometimes even if i really like the table i will) If they are being rude, have a condescending tone of voice, or don't even say thank you, it's hurtful and I have learned not to take it personally, but it still gets to me sometimes.

I have never ever done anything to anyone else's food, but I have seen it done (they were always above and beyond obnoxious for this to happen), and its usually the back of house that gets mad that the server is upset and does something about it, not the server doing it.

Either way, be nice, courteous and appreciative, and tip appropriately. I expect 20% and it is amazing how many people don't do this.
When I go out to eat, I tip a crazy amount, 20% if the service isn't even good, and 25-30% if it is.
I don't usually send back food, but I will if I just can't eat it, and I'm super nice about it, explain that i'm also a server and understand it's a pain. That usually gets good results, and sometimes some extras!