A LOLcock is a laugh-out-loud worthy penis; it can be judged so based on it's size (diminutive or outsized), its appearance (most any tattoo would count) the hilarious predicament it's been placed in (with a hat, perhaps).
When a female is "going downtown" on a male, you distract her. As she looks away, you slap her in the face with your manhood, while shouting "Lobcock!"
Me: Dude, I got with Sarah last night!
Friend: Uh...doesn't she have a bulge though? The fuck is that?
Me: No, it's just her lobcock! It's like 2 inches!!
Friend: huh, isn't that the size of your d--