"Drinking Codes" joke

A brunette, a redhead and a blonde walk into a bar. For the
sake of brevity, each one orders her drink with an abbreviated
code word. The brunette walks up to the bartender and says,
"Hey give me an ML." The bartender nods his head and hands
her a Miller Lite.
Following her, the redhead walks up to the bartender and says,
"I'd like a BL." Giving her a nod, the bartender pulls up a
Bud Lite.
Last, the blonde walks up to the bartender and says, "Give me
a Fifteen."
"A Fifteen?" the bartender replies, "What the hell is that?"
"Oh, you know," the blonde says, "A Seven and Seven."