I agree.
It is OBVIOUS to anyone marginally involved with a wedding that there is no wiggle room for a crasher. You pay per person, seating charts are arranged in advanced, even a last minute additions have place cards.
This turkey is beyond believable. If anything it points out how hollyweird does not exist in the real world.
The could have done the brain surgeon crasher about a pair who crashes operations and pretend to be brain surgeons.
LOL...I like the sound of your movie scenario better.