They don't actually like your band, blog, or screenplay.
All photographic evidence of their awkward phase.
The way they eat when they're not with you.
They don't exclusively wear sexy underwear.
They've stalked your ex on Facebook.
They're not nearly as sophisticated as they let on.
This is not how their bathroom normally looks.
They neither love to cook, nor are they very good at it.
They don't hang out at home in their coolest clothes.
The biological reality that they poop.
They haven't farted in front of you either.
They're not really this much fun.
They're a poor loser.
They're not actually this into sports.
They're not always "on."
They're not this nice, either.
They don't, in fact, love sushi.
They actually hate Sex and the City.
How many people they've been with.
Their irrational fear of cotton (or some equally weird quirk... we've all got one).
They have serious morning breath.
The good news is that you have just as many things you're afraid to let them know about.