The Big Bang Theory, Season 4

[Sheldon has joined Penny, Bernadette and Amy Farrah Fowler on their girls night out at a bar]

Penny:
Sheldon, have you ever kissed a girl?

Sheldon:
Other than my mother, my sister and my mee-maw, no. But in the interest of full disclosure, I was once on a bus and had to give mouth-to-mouth to an elderly nun who passed out from heat exhaustion. Every year I get a Christmas card from her, signed with far too many X's and O's.

Bernadette:
That doesn't count! Aren't you even a little curious?

Penny:
Yeah, you're a scientist, where is the curiosity?

Amy:
I'm available for experimentation [turns towards Sheldon and puckers up]

Sheldon:
Thank you, but not necessary. We know everything there is to know about kissing. It requires 34 facial muscles and 112 postural muscles.

Amy:
Oh, blah, blah, blah. Give me some sugar, bestie. [turns to Penny and kisses her, all three girls start giggling]

Sheldon:
I'm certainly glad no one said they were curious about Aztec human sacrifice.