Fancy buying me a drink?

This guy standing at the bar when a girl came up to him.

"Fancy buying me a drink?" She said.

"Sure," he replied. "If you let me choose."

"Okay," she grinned. "But how will you know what I want?"

"Well, it's kind of a talent," he smiled. "All I do is look a girl up and down and I know exactly what drink suits her best."

"Okay," she giggled. "You can choose for me."

So he turned to the barman and said,

Spoiler:

"Diet coke, mate."