I don't think that's always the case, but in the case of men, I suppose they tend to be more visual. Regarding wearing makeup, it doesn't necessarily have to do with impressing boys; my wife likes to wear makeup at home just to feel pretty. She isn't necessarily trying to impress anyone, although it could be for me too. I suppose you could say that boys lie for that reason; they're just trying to appear more confident. It's not only boys that tell lies, however. A lot of idioms are hasty generalizations, in my opinion. I'm overanalyzing this; can you tell? XD