Place it after the visual gag is established, then follow it with the Danger Alarm Meme Sound Button if the scene escalates, or the Roblox Oof Sound Button once the character finally reacts and takes the hit.
Über diesen Sound
A five-second voice clip where a man calmly states, Excuse me, you are on fire, as if reporting the weather. The humour comes from the complete understatement, turning a moment of panic into something dry, awkward and oddly polite, which makes the warning feel funnier the more serious the situation looks.