It depends on many factors - how bad was the problem and whose problem was it? If it's poor service accompanied by poor attitude then it's always reflected in the tip. On one occasion, I left a penny tip while using a credit card, service was horrendous, slow, inattentive, the wrong order was delivered and no apology or commentary offered by the server. Didn't bother to ask me if everything was alright so in this case I didn't offer. This was many, many years ago, today I would have asked to speak to the manager. My last run in with bad service was at one of the steak houses here in DC, I'd been there before but it's not one of my regular haunts. My wife and I were never offered water and didn't recieve it after we asked for it when placing our order. After about 20 minutes we tagged a busboy and asked him to bring us some water. Timing was off on delivering the food, might have been a kitchen problem but we didn't see our server for about 25 minutes. Doing the math, it was about an 80 plus minutes before we saw our main courses, during which time we saw our server twice - once when ordering and after the mains were brought out- the appetizers were brought out by someone else. In this case, I asked for the sommelier to stop by our table. When he stopped by I let him know that service wasn't very good, my wife's steak was overcooked and I didn't plan on leaving the server much of a tip and tipped him well and directly as he had been friendly and provided a good recommendation. He apologized and brought us a $100 gift card, which I later re-gifted to a co-worker. Left the server a 10% tip. If the problem is with the kitchen and not the server, then I'll let the manager know and the tip is not impacted. Cheers, Jeff