Sometimes it's hard to know whether being practical outweighs being polite. Here's the situation: You spent a good amount of time during the reception chatting up the bride and groom. You congratulated them on their new marriage. You told the bride how beautiful she looked. You sampled the fare and sipped the couple's signature cocktails. You even rocked out to a Katy Perry song with the bride on the dance floor! In short, you've been a stellar wedding guest, but now it's close to midnight and you've got a long drive home.
You'd love to give them one more hug and reiterate how awesome their wedding was, but there's already a long line of well-wishers waiting their turn to say goodbye. Should you get on line and hope it starts moving fast, or is it okay to make like a ghost and disappear? You're pretty sure the bride wouldn't be offended or even notice. It's a common problem plenty of guests run into, but most guests don't know the etiquette of making their exit.
If you already offered your best wishes and had some alone time with the couple, it's fine to leave without saying goodbye. According to wedding etiquette rules, it's acceptable for a guest to exit a reception once the wedding cake is cut; saying hasta la vista before then is considered rude. So if your situation is anything like the above, you're in the clear. A wedding reception isn't like a house party, where you'd never leave without thanking the hosts and saying goodbye. With the sheer number of guests at most receptions, it would be impractical to expect that each one of them will tell the bride and groom goodbye. That's not called good manners—that's called paying overtime!
But let's say it's early on in the evening, the cake hasn't been cut, and you haven't had much facetime with the bride and groom. In this case, it's important to find the couple and thank them for having you, explain why you need to make your exit, and congratulate them once more. Luckily, this should take just a few minutes at most, as the couple will want to get back to enjoying their party.