Probably an old one:

[RichardW]

An Irish woman of advanced age visited her physician to ask his advice on reviving her husband’s libido.
‘What about trying Viagra?’ asked the doctor.
‘Not a chance’, she said. ‘He won’t even take an aspirin.’
‘Not a problem,’ replied the doctor. ‘Give him an ‘Irish Viagra’. It’s when you drop the Viagra tablet into his coffee. He won’t even taste it, give it a try and call me in a week to let me know how things went..’
It wasn’t a week later when she called the doctor, who directly inquired as to her progress.
The poor dear exclaimed, ‘Oh, faith, bejaysus and begorrah! T’was horrid! Just terrible, doctor!’
‘Really? What happened?’ asked the doctor…
‘Well, I did as you advised and slipped it in his coffee and the effect was almost immediate. He jumped straight up, with a twinkle in his eye
and with his pants a-bulging fiercely! With one swoop of his arm, he sent me cups and tablecloth flying, ripped me clothes to tatters and took me then and there passionately on the tabletop! It was a nightmare, I tell you, an absolute nightmare!’
‘Why so terrible?’ asked the doctor, ‘ Do you mean the sex your husband provided wasn’t good?’
‘Freakin’ jaysus, ’twas the best sex I’ve had in 25 years! But sure as I’m sittin’ here, I’ll never be able to show me face in Starbucks again.