Don't slip him a note. Talk to him in person. Writing him a note is just about as bad as having someone ask him out for you. If you can't speak to him in person [Even if it is about a touchy subject], how can you ever hope to have an open, honest relationship?
I personally would never have the confidence to ask a guy out - and besides, I'm old-fashioned. But if you wanna ask him out, I say go for it. More power to you. :]
Just bring it up casually. And don't use the term, "wanna go out?" It sounds too pressuring. Just ask if he wants to hang out sometime. But be specific - have an event and a date already set, so it actually HAPPENS. Just saying, "Wanna hang out sometime?" probably won't get you anywhere. He'll say, "Sure," and then nothing will ever happen.
Instead, say, "Hey, wanna catch a movie with me this Saturday? I think THIS MOVIE is playing..." or something. That way, if he says yes, you have plans and nothing needs to be sorted out. And, the date can't really be avoided.
Be sure to prepare yourself for rejection though. If he says no, he says no. Dust yourself off, and stay friends! If it doesn't work out, don't stop talking to him - talk about awkward.
Hope it all works out for you. :]
