Doesn't have to be a pilot, any aviation person with the courage of his/her convictions can, and should, step up to the plate. But you had better be right.
In the 1970s an RAF Chief Technician, settling in his seat at the back end of a DC-9 at LAX, bound for somewhere else on business, saw a loose panel or something in the intake of the starboard engine just outside his window. He called the CC and was fobbed off with a "Oh I am sure that's alright, please sit down Sir" (and with it an implied, "...and shut up").
He stood up and created a huge scene, to the extent that the captain was summoned to deal with him. Recounting first the CC's reaction, he pointed to the offending article out of the window. Long low whistles, mumbled apologies, glares at the CC and thanks were then the order of the day.
I don't know if the airline concerned (which I do not remember) refunded the RAF his fare. Probably not.
On the other side of the coin, a young RAF officer made a flash call to air traffic to stop a Britannia as it took off, because he thought the controls were disconnected. He didn't know that the Brit had servo-tab controls which floated disconcertingly once unlocked until the air speed straightened them out.
As I said at the start, you had better be right.