A pal of mine was bought a pint by an audient who asked him to sing 'Down where the drunkards roll'

My friend said he'd do it shortly & the audient wandered off.

He performed the request, but some time after, the requestor came over & asked when he was going to do it.

'I've done it'

'Well I didn't hear you'

'Well I'll do it again later, ok?'

My friend ended up doing it 3 times, but the other bloke missed it every time!