One of the first thing that any new server learns, both in and out of the catering industry, is that when a customer tells you that he's a generous tipper, you're going to find a handful of pennies waiting on the table when the meal is over. Over the years, servers develop a keen, almost supernatural sense for the kind of customers who tip poorly and (even worse) the customers who think they're great tippers but aren't. And customers get treated accordingly.
The old tipping intuitions kick in even at catered events where tipping isn't necessarily expected. If you're getting bad service, do a quick breath check (you never know) and then find an excuse to ask for a special favor you can tip for, like a lemon or cucumber slice for your water. You'll get treated like royalty the rest of the night.