Cross paths
"the PILOT is the boss of the plane"
The BOSS is boss of the PILOT, his career and future. "If you can't do it then next time we'll find someone else who can" is the usual threat.
If same situation arises and you think you have a DO IT BOSS on board, get him up front for a minute to see fog and confirm YOUR call. After witnessing the situation himself he should back off and understand. If he still disagrees advise him he is welcome to identify himself directly with ATC to advise his landing intentions on his authority.
DO IT BOSS's are big on bullying but cowards on public blame.
Regardless, up here PILOT is BOSS, so divert to X, make a report and live to get another job...