St. Louis, We're Not

I could understand if, in a crowded subway, someone reached down and grabbed the wrong bag. Wooops. It would all be vaguely scripted:
"Oh, sorry. I thought that was--"
"Oh! Right! Ha! Well,--"
"Well--"
"No, you go ahead."
"Ehhh..."
[fumbling exchange of phone numbers or fisted cuffs depending on how the dialogue plays out.]
What I can not understand is crashing a wedding in your jeans and construction boots, proceeding to the dance floor, making out with your date (similarly clad and coiffed), and slopping back to the side of the room where you pick up my camera bag-- MY-- CAMERA BAG.
What. The. Hell.
I stand up from the table and say, for lack of better idea "Hey! That's my stuff."
Barfly McStickyfingers steps back and leaves.
And then he comes back three times.
He brings friends.
When they are asked to leave again and again, they do, but not without a fight. They insist that they were invitees. Matt, in his infinite compassion, tells the guy to, "Get out or I will throw you out." Plus a couple of bad words.
Bride Sarah calmly ignores the distraction and dances on.
I have another glass of wine and hide my bag.