Called Billr, the 99-cent app -- a lot cheaper than covering your friend's glasses of 2010 Calera Viognier -- lets you choose the size of your party, then punch in the applicable items for each person. The app then calculates tax and tip separately, with those numbers being adjustable for what state you're in and what kind of a cheap bastard you are. You then get the individual results, which you can then share by either passing around your phone or by texting or emailing the information to the guy ignoring you across the table. No more confusion, polite or otherwise.
The app works for up to 16 people (time to head to Park's BBQ) and is available on iTunes.