A sword & sandal type movie. The hero is visiting a king who demonstrates his power by having two of his flunkies hang themselves. They do so within seconds, and with no second thoughts. I don’t remember how they affixed the ropes, but it was fast. The movie was probably 70s or 80s.
I don’t know, but I feel like someone asked this same question not all that long ago. Hmmm…
The Beastmaster is probably the movie you’re looking for.
Relevant TVtropes link:
The Beastmaster maybe.
I found this entry on tvtropes:
" In the movie The Beastmaster High Priest Maax orders two of his underlings to kill themselves as a show of his power by hanging themselves. They immediately obey."
Under the trope, Ordered to die.
Curses! Ninjaed by Yamato Twinkie
And the relevant Beastmaster scene is here (starting at 3:28):
Found it. Not only did somebody ask this already (last November), it was you.
And it was answered then too.
Write it down this time, man! 
Well, that’s embarrassing! I swear on my mother’s grave that I’ll never ask again 
eta: my mom was cremated, so I may have a little wiggle room.
It happens. I’ve forgotten things I’ve asked here and asked them again too.
And I probably didn’t write down the answers the second time either.