DOCKINEZ: very advanced joke
This is a British wordplay joke. Here’s the breakdown:
“I’ve been hit by a bin” — the person is reporting that a rubbish bin (trash can) struck them, as in a literal physical collision.
“I don’t think you have, mate” — the response sounds like a dismissal, but it’s actually a pun. In British slang, a “bin” can also refer to a dustbin lorry (garbage truck), but more importantly — “been hit by a bin” sounds almost identical to “been hit by a been”…
Actually, the core pun is simpler: “bin” in British English is also used in the phrase “wheelie bin”, but the real joke is that “I’ve been hit by a bin” sounds like “I’ve been ’it by a bin” — and “been hit” ≈ “bin ’it”.
More precisely: the joke plays on “bin” sounding like the past participle “been”, so “hit by a bin” = “hit by been” — grammatically nonsensical, hence “I don’t think you have” (you haven’t “been” anything, grammatically speaking).
The bearded guy is essentially doing a grammar correction disguised as skepticism — a classic dry British humour move.