When the DM says, “Are you sure?
The new player says, “Yeah, why?”
The experienced player is already running.
Honest to goodness, this actually happened at my last session. The party were fighting this dragon, and in the previous round the Eldritch Knight had thrown his dust of dryness into the dragon's mouth.
The Eldritch Knight and Lore Bard are new players, while the Land Druid and Thief Rogue have played 5e before.
EK Fighter: I want to retrieve that pellet.
Thief Rogue: Are you crazy!? He didn't recharge his breath weapon this round!
Land Druid: Yeah, and I've already lost one death save over here! Just kill it!
EK Fighter: But if I get that pellet back . . .
DM (me): *clears throat* Yeah, um, let me read you the disclaimer in the Player's Handbook.
Wizards of the Coast is not responsible for the consequences of splitting up the party, sticking appendages in the mouth of a leering green devil face, storming the feast hall of a hill giant steading, angering a dragon of any variety, or saying yes when the DM asks "are you really
sure?"
*everyone bursts out laughing*
Lore Bard: *smacks the table* best moment of the night!
Land Druid: 40 years I've been playing this game, and that's the first time I've seen the DM read the disclaimer aloud!
EK Fighter: My mistake. Okay! I'm gonna hit this thing!