It's been my experience (as both customer and server) that typically, when splitting up a check at the table, people tend to underestimate their portion (and account for the gratuity) accurately. A legitimate mistake on some people's part, an easy way to cheap out for others. Whenever I see pen and paper coming out, or even a calculator, I knew I'd be in for at best 10%.
My wife and I have been friends with a couple since college. I love them dearly, but going out to eat with them was always a pain in the a$$. They would never chip in enough for the bill, with my wife usually putting in more to make up the difference. The irony of it all is that they think (to this day) that we are the cheap ones! When we get together nowadays, they quickly express to the server that separate checks will be required. Fine by us...

Fine, never go out to eat in a group greater than 6 and you will be okay.

Clearly you never waited tables and don't know what you are talking about on the matter.

I got screwed not doing the automatic gratuity one time. Waiting on Willie Brown, former Duke of California, told him up front the policy was to include the tip, but I like to earn my money. He got good service and stiffed me, wearing a suit that was worth more than my car at the time. He asked for be next time he came in and I refused to serve him.
Are you familiar with the term, "tragedy of the commons?"

It's the booze! fast food with booze!

I always tip 20% maybe less if the service is really, really bad...

When out for food in S.F. with a group of six... bill plainly said 18% gratuity added... I paid the bill with no added tip and we walked out... waiter chased us down the sidewalk screaming we didn't leave a tip... I pulled out the bill, pointed at the 18% and started to get in his face... my friends pulled me away.

Who was wrong here?

Thread hijack...

I also have some people I hate going to dinner with. They always want to split the bill 50-50 regardless of what they ate, so inevitably, you find yourself ordering more than you want because you don't want to feel gipped since you don't want to look like the cheap one saying they owe more. We haven't gone to splitting the bill checks yet.

Yea, I know a couple like that. They always order an expensive appetizer and eat two bites and leave the rest for the "doggie bag." Then order the most expensive meal, lots of drinks and think a 50% split sounds good. I had a $12 meal and water. I threw a $20 on the table and said that will cover my 12 buck meal and a nice tip. They were horrified. After that we asked for separate checks.

I am a good tipper. I don't have a fixed percentage. At a cheap breakfast place with a $5 meal I am not going to leave just a buck. If there is a automatic tip of 18% that is all they get. I usually go for 30% for good service. I had a good meal with HORRIBLE service and I went looking for the manager. It was perfect, he was talking to my waitress. I told them both that the service was horrid and I was tipping one penny and that was more than enough.

I witnessed something very similar when I was waiting tables in college. The server was irate and demanded to know if god had a $300/month car payment.