Stupid things in Films and Television:
Scene: A covert team of special forces operatives rappel from a helicopter into the middle of a jungle teeming with hostile guerrillas. And then have a team briefing, which they should have had earlier back at base, like real special forces do. There is a row over something trivial.
Scene: A gang of people meet in an abandoned warehouse full of old containers and racks with plastic sheeting. Lots of people burst in and fire machine guns without seemingly aiming at anything and oblivious to the prospects of ricochet and collateral damage. Nobody appears to get hurt except the baddies. Ammunition magazines never seem to empty, unless it just happens to be at the 'wrong' moment.
Scene: A Love scene that lasts too long. Yes, I know what they're doing. You don't need to go on about it.
Scene: A man gets knocked out with a single punch. Then recovers a few minutes later. Er - No. That's a trip to hospital with suspected concussion.
Also: Incidental music that's supposed to raise tension. No it doesn't. It merely signals that something horrible's going to happen.
I've given up on cups and pens changing hands, long hair going down the character's back, then on their shoulder, then down their front. People not locking their cars. People opening their front doors wide without checking first. Telephones being answered on one ring, or not being answered during high-tension situations. Maverick cops. etc etc.