Apparently the word hola, although technically proper, is not typically considered a masculine thing to say. Upon greeting a passing Mexican co-worker with this expression, his response was

¡No, no, 'hola' es para niñas! Los hombres se dicen '¡Que pasa!'

(Translated: "No, no, 'hello' is for little girls! Real men say 'What's up?'")

So there you have it, another item in the long list of things you never learned in Spanish class.