Scuba diving

[rebbonk]

Two Brummies were sitting quietly over a beer on a shoreside bar patio.

As they witnessed two men in a boat preparing scuba equipment, one had a thought:

'Jim, why d'ya spose scuba divers always fall backward into the water?'

'Fred, you idiot -

Spoiler:

if they fell forward they'd still be on the damned boat!'