I did this in Germany.
We (2 of us guys, 3 girls) were going to visit a concentration camp in Germany (I know.. heavy shit), and the nice hotel we stayed at was hosting an authentic german wedding (They have a big ass log, and a two sided saw, and the groom and bride go back and forth till they cut the log. Symbolising their relationship or something) It was really cool too see!
Similar to this shit:
We were on our way to the hotel bar, grabbin some drinks, when they moved the wedding party to the bar. We ended up taking pictures with the wedding party, went around and talked to people in our broken German. We ended up getting trashed with the wedding party and everything. Everyone was loving us Americans, teaching us drinking songs and what not. Definitely one of the better cultural memories from my 4 months abroad. Even the little kids drank! They have some drink where they mix sprite with a little bit of beer for youngins. It was so different than what you see here in the States.
Thats the only time i've "crashed" a wedding. I didnt get laid or anything, but it really was similar to what Wedding Crashers did. By the end of the night, everyone knew who we were (not cause we were hammered Americans, but because they were legitimately enjoying our company).