Do guys actually whip it out and measure it with a ruler?

I assume you know what I'm talking about...

They sometimes brag or just mention how many inches. But how do you know exactly? Excuse me for being blunt but I gotta know.
Update: And I'm a girl by the way. Not trying to disguise myself as a guy... I don't know why you thought that.
Update 2: Some of these answers really made me laugh.

And shut up, Quagmire. I see that on every freaking post.
Update 3: I see how it is, Jerry...
I see how it is...
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