There is a specific region in the human brain that is responsible for handling judgment, and under normal circumstances, it lights up like the flaming runway at the end of Die Hard 2 when we're presented with a new situation that requires immediate evaluation, such as meeting somebody for the first time or trying to figure out whether we like the changes to the TGI Fridays menu or if we should flip the table over and go to IHOP instead. We are judgmental creatures by nature, and we are eager to criticize. However, when we're infatuated with something, that judgment-casting region of our brains goes completely dark like a rolling blackout.
We actually become physically incapable of detecting the flaws in the things we love. Apparently, human biology believes it necessary to throw the blinders on in order for our species to survive -- we have a biological imperative to lower our standards.
If unicorns weren't so high and mighty, they'd still be around today.
There is another phenomenon related to this love-blindness called the halo effect, and amazingly it has nothing to do with eliminating your dating competition with a pair of dual-wielded needlers. The halo effect refers to our habit of extending one positive quality that a person possesses to the rest of their character, basically giving us an excuse to like that person. When your friend laughs at the hot girl's terrible joke, he's not faking it -- his brain is telling him, "This person has what you look for in a mating partner, therefore from now on, every little thing she does is magic."