You know you're sleep deprived when...
... you are trying to purchase something online, you go to type in your address for shipping, and you can't remember your own zip code. So you have to go into your junk drawer to find one of those return address labels your auto insurance company sent you as a "thank you" just to figure out your OWN address. You think to yourself that you should really send your insurance company a "thank you" for helping you know where you live, but sending them a thank you note would require you knowing yet another zip code. And really, one zip code is hard enough.
... you spent about thirty minutes one day cleaning up a pukey, poopy baby, requiring you to call your husband home from work and do major bandage repair. Several hours later, when you go to throw something away, you discover that amidst all the chaos you apparently threw one of your child's six wearable onsies in the trash and have to fish it out, because, obviously, you cannot distinguish between it and a poopy diaper.
... you are half asleep (and trying to blog and watch Grey's) while you are cutting Tubifast. You look down to see that not only have you cut your four hundredth piece of Tubifast, but you've also cut the draw string off your pajama pants.
... you are watching a Braves game where they mention a Matthew West concert. When they give his web address, matthewwest.com, you comment to your husband how weird it is that he spells his Matthew with two t's. "Two T's? Who does that?" you say in disbelief. "That's rare." Your husband looks at you like you're crazy. So you say, "Is that how you spell YOUR Matthew?" He comments that, yes, that's not only how HE spells HIS Matthew, but also 90% of the Matthews in the world. He holds it over your head for the rest of your life.