I've heard it happens from time to time. Not on the grand scale that the movie portrays it to be. A catering hall might be holding more than one wedding at the same time. A guest from wedding number one, just might wander over to wedding number two just to take a quick peek. (No, I've never done it)
Come to think of it, I did once crash a wedding party near San Bernardino. I didn't plan on it. I was had a meeting with someone at a hotel and when we got done, we noticed a wedding reception in one of the big rooms. So I just entered it (for the refreshments, not the chicks) and loaded up on food and drinks. It was a Latin wedding so the folks there liked that an obvious gringo could speak their lingo so I guess they didn't mind that I was crashing them.
We need to have Clemenza crash several weddings, using these rules, and then report back on how he made out. One plus for Clemeza is that he knows a lot about fine wines and can impress the chix with that type of knowledge. Go for it, Clemenza!