I know of a situation where a plane (737) landed so hard the nose gear axle broke....
One tire went bounding down the runway to get ingested by the left engine, the other got ingested by the right.... Fortunately, they just slid to a stop on or near the runway with some pretty extensive damage...... But that easily could have killed everyone onboard.
Why?
Because as the pilots broke out, one said "I got it."
The guy who said it meant "I have the runway in sight."
The other guy released controls because he thought the "I got it" meant the other pilot was taking control of the aircraft..... So the plane touched down with both pilots thinking the other guy had the controls.
Easy to see how bad things happen if the wrong thing is said at the wrong time. And "go around" from a jumpseater is always the wrong thing.
-Of course we can all imagine situations where the jumpseater would need to say something..... I would recommend "check your glideslope" or "you are unstable." Nothing wrong with speaking up, just don't use the exact phrase another pilot would use to trigger any maneuver.