In a Rush

Everyone, get out of the way! I need to leave this building as quickly as possible. No time to do calculations! I also can’t take out my wallet and leave a couple of bucks on the table for some strange reason! I need to get out! Stat!

This doesn’t sound very reasonable, and if this diner had enough time to write this message down, they definitely had enough time to tip. Were they worried about at what percentage to tip? Well, it’s not like we’re all carrying calculators in our pockets now, right? And for a $99.25 bill, why not round up to $100 and calculate in your head? Impossible, because they were in a hurry.