Are you trying to make a penis emoticon? For those isn't it more common to use <==8?

Miles, yards, feet, inch or kilometres, metres, decimetres, centimetres?

Might be planck volume or liters or fluid ounces.

Cubic kilometers might be right out...

I really don't get it but I giggled.
I wish I was better at math for half of these but I'm majoring in biology so that is about to change. :D

Plank units

http://en.wikipedia.org/wiki/Planck_units

It could stand for Limit

L definitely means Length, people.
Seriously.

He's saying his wang's length is 8, and she's implying that he must not be talking inches, because it's actually much shorter, hence the joke.

Nah n47h4n, L could be liquid, hence volume.
L could be liter, again, volume.
L could be Avogadro's constant, which is moles.

She could have been talking about liquid volume, hence another interpretation of the joke.

You guys are definitely overthinking this. Nathan got it right, the joke is comparing 8 cm to 8 in.

Nobody measures their penis in liters or moles, and L usually stands for length anyway. Seriously. you could say L is in velocity, but that wouldn't make any more sense than moles.

Such a wonderful reply :D I'm totally nabbing it ^^

Ross, who measures their discharge in cm or in? Nobody measures their liquid discharge in cm or in. That doesn't make sense. Moles of carbon in the discharge is valid. You know fluid reservoir...

L is velocity of discharge so that you can determine the minimum thickness of the condom. Seriously.

No, it's definitely talking about length. Lol, it's funny.

Obviously, they're talking about pressure. Pa, kPa, atm, or bar?

astronomical units!!!

the discrete metric!