Fighter: I punch through the glass to kill the monster.
Me, the DM: …you want to punch through reinforced bullet-proof glass, of which the monster sprayed with acid on the other side.
Fighter: Yes.
Me: You know what? Fine. Roll for strength.
Fighter: *Rolls the first Nat20 of the campaign*
Cleric: Oh my god-
Me: Somehow, despite the fact that this glass is fucking bullet-proof, you manage to shatter it with a single punch, and you kill the monster the second your fist makes contact with its face. Congratulations.
i mean… the DM could have said the acid the monster spit made the glass weak enough to be punched through.