This reminds me when I was on a SJO-SAL flight and this guy gets all fired up because someone "was" on his sit calls the FA.

He yells out his point to which the FA grabs his boarding pass and says to him:

"You are correct sir, that is your sit number, however this flight is going to SAL and you should be on the CUN plane right next to our gate."

The laughs of the other passengers that were close to witness this and the expression on the passenger was priceless.