I used to have really curly hair, and then I got my first haircut (I was about six or so) and then it went straight. Then a few years later, I shaved it. And it came back wavy and curly.
Now, it all depends on whether or not I've brushed it. If I don't brush it, it stays wavy with some curls here and there. Once I brush it, it goes a bit straight. If I brush it when it's wet, it goes completely straight. My hair is so long, so if I brush when it's wet, it's too heavy to pull itself back up into the wave.
I know this a question to the ladies - but I'll chime in, My hair is wavy - but after 23 years of marriage I'm not sure about my wife! She's always styling it with curling irons, curlers, teasing and other techniques.