I tip and adhere to the 15%. However, I don't think twice about giving a lower tip if warranted; sometimes none. A tip is a tip. If you do not serve me to my satisfaction, then you aren't earning your 15%.
The biggest problem I have with tipping is gratuity. Gratuity is complete bullshit. Not because of a fixed 18%-20%, but because it gives the waiters a get out of jail free card. They can slack off and not care as much about your table because they are 99% of the time guaranteed to get that tip. A lot of establishments will not even waive the gratuity no matter how much you bitch. It's fucked.
This is one of the very few cases when you can tell your boss off. Not sure what state you are in, but you can always threaten labor laws against him and file inquiries with the state. I am pretty sure it won't cost you a thing and possibly get money out of him if you can prove he never paid you for overtime.
Just call it an ATM; "machine" is in the name! Same thing with PIN.
"Could care less" as mentioned above.
People who put the dollar sign on the right (wrong) side of the number (1$). Sorry, but if I can put your currency symbol on the right, you can put mine on the left. Pretty sure I have seen people from America do the same thing which is sad. I have also seen people try and use the cents symbol and end up doing ¢99 instead of 99¢. Sometimes they also like to add an arbitrary decimal to beginning of the number which would lead me to believe that it is less than a single penny. Dollars on the left; cents on the right and no decimal point!. Thank you and you're welcome.