He:
(Watching me scroll my tumblr dash) What's with all the cats?

Me:
What?

He:
The posters of cats with words on them.

Me:
Ohh. LOLcats? Umm... I suppose it's a nod to the prevalence of cats as a common subject of internet output combined the degradation of the rules of spelling and grammar on the web? And you know, the more times you see something it becomes funnier, and then sort of a shorthand for...nevermind. I actually have no idea.

He:
Yeah. I just don't get it.

Uh:
(You try to explain it. Luckily there's a 7-page wikipedia entry on lolspeak complete with the tidbit that the first "cat macro" was made in 1870. O RLY?)