Metaphors:

I see this line in profiles a lot, or something similar: IM me, I don't bite. That's a metaphor or a simile. They're making a comparison with a dog.

In my opinion, their profile would be much funnier if they expanded on the metaphor. For example, something like this:

IM me. I'm friendly. I will lick your face, sniff your crotch, and if I like what I smell, hump your leg. If you're lucky maybe both of them.

It's the unusual comparisons that make a piece of writing interesting.