Not Tipping
OK, this one seems totally obvious, but let's talk about why waiters hate customers that don't leave a tip. The truth is that servers' livelihoods depend on tips for the most part because, at least in the United States, most of them are paid less than minimum wage.
Every country is different and even tipping customs vary from culture to culture, but if you're in the US, there's a very high chance that your waiter is really counting on that tip to make ends meet.
Stacking Up Plates
This one might be a bit surprising because most people who stack the plates after they are done eating think that they are doing their server a favor. However, many waiters don't really like it.
This is because a lot of waiters have a system for clearing the table and if you stack up the plates your way, that might mess up the system they have. Just try not to leave a huge, gross mess and let the server do their job.
Not Making Eye Contact
Eye contact makes a lot of people uncomfortable so if it's really hard for you, don't worry about it. However, it is important to remember that waiters are people too and like to be treated just like everyone else.
Waiters hate when people just ignore them and not make eye contact with them. Sure, they're doing their job, but it doesn't hurt to look at them in the eyes and thank them for their service. Look at them especially while you're ordering!