The phrase let's have it is long standing British slang for bring it on, often heard at football grounds, in pubs and in playful confrontations. Online the clipped shout, with its drawn out final t, spread as a short form reaction sound on soundboards and in meme edits. Its appeal is its brevity and tone, half challenge and half joke, so creators reuse it wherever a moment needs instant bravado without a long setup or explanation.