Coming from a background in law enforcement, I can provide some context as to why it’s fake aside from the bad acting.
Undercover FBI badge like his is not authentic. Beyond that, it would be very detectable under a thin tshirt and therefore not very good cover.
No law enforcement official would allow a potential suspect to unbuckle his belt, stand-up and advance towards the officer and reach into his shirt. That would never happen.
This is a ridiculously fake video. First you can tell it’s a fake plane with the most generic 1970s flight attendant costumes they could find. FA’s don’t go around IDing people on the plane. There is no scenario where the FBI is going to be conducting an undercover operation on a flight, but if an armed FBI agent was on the flight the flight crew would know about it. If for whatever reason that FBI agent was being enough of a jackass that the cops were called his status as an FBI agent is irrelevant, despite what some people think Federal agents don’t “outrank” municipality cops and don’t have the authority to dismiss cops that are conducting a lawful investigation. An FA has no way of knowing someone is flying one way without luggage and if that person was flagged for some reason he’s getting grabbed before he reaches the plane. It’s also highly unlikely a male agent will have hair that long even if they’re conducting uncovered operations.