My two things:

• “What’s the order when you go through the door?” writing on notepad, then stopping “So the wizard is in the middle? Okay…”
• We play with maps on a TV and I usually add numbers to the bad guys for clarity in a battle. They were going into a dungeon and ran into six small shrubberies that ate their lunch. Came close to a TPK ‘cause they were cocky. Lesson learned, two rooms later they go into a room they can only see half of. In that half are four of the shrubberies numbered 1, 2, 24, 25. The bard: “Holy shit! There are TWENTY FIVE of them in here?” They were quite surprised that they couldn’t find the other 17 since there were only 8 of them.

You feel you are hidden

It seems like they are telling the truth

It appears to be free of traps/alarms

It looks like they believe you

Do you [insert object interaction here]?

You don’t see anything happen

I also enjoy building tension and then releasing, while occasionally building and then giving them jump scare. I did that recently playing Mothership. Earlier in the session two androids were working on repairing a doodad while the Marine stood watch outside the room. When the Marine steps back in the room they see one of the androids in the chair that was occupied by a body a couple of hours earlier

Marine: What happened to the body that was at the console?
GM: As you think that you turn your head to the left, and that side of the room is empty. You whip your head to look on the right side of the room, and in the corner closest to the door
Marine: I RAISE MY SMG
GM: and you see the body of the lieutenant laying flat on the ground, where the androids had placed it so that the body wouldn’t get in their way

Later, while exploring another area:

GM: Your light cuts through the sudden darkness. As the beam crosses the floor you notice the body that was in the middle of the hallway earlier is no longer there. You swiftly swing your beam left and right, looking for the body. As you turn around the light illuminates a figure standing a few feet away behind you. It’s Rico the Android. As you slowly breathe out, tension leaving your trigger finger, you feel something drip onto your face. You look up as something falls onto you. Roll Panic

My mom’s favorite is the phrase “nothing discernable happens.”

I played with a DM that asked every time “which hand did you open the door with?”

Gave us a complex in the best way 😛

Also a classic for a failed perception check, particularly when there is no trap: “You don’t see the trap”.

Player: “Guys, this is where the assassin is supposed to be hiding out. I’ll bet he has it trapped with poison darts.”

GM, feverishly scribbling notes: “Anything is possible”

Bobbins searches the cave.

It’s also fun to pass a “nothing interesting” note privately to the rogue (especially if they’re playing some variety of an untrustworthy scoundrel).

The party jumping at shadows tend to make the rogue’s player grin smugly, which sometimes makes the party jump even harder at shadows.

That’s why I roll to call bullshit on the DM. And fail.

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This is where it’s fun to be playing a character who is oblivious or dumb. You can confidently do things that the metagamer in you says not to.

If your players are doing meta playing to get an advantage, the problem is the players.

You’re trying to make a story for everyone to have fun, they’re trying to “win” the story by ruining the fun of it.

Either they fix their behaviour, or they fuck off. Having to create measures and countermeasures against your friends because their oversized ego doesn’t let others enjoy a game is a bit pathetic.