"Double Martini on the Rocks" joke

A business man enters a tavern, sits down at the bar, and orders a
double martini on the rocks. After he finishes the drink, he peeks
inside his shirt pocket, then asks the bartender to prepare another
double martini.
After he finishes the second one, he again peeks inside his shirt
pocket, and asks the bartender to bring another double martini.
The same pattern is repeated a few rounds; the business man drinks a
double martini on the rocks, peeks inside his shirt pocket, and orders
another one.
Finally, the bartender says, "Look, buddy, I'll bring you martinis all
night long, no problem with that. But you just gotta tell me why you
look inside your shirt pocket every time before you order a refill!"
The man replies, "Oh, I'm just peeking at a photo of my wife. When she
starts to look good, then I know it's time for me to go home."