How do you respond to a text from someone you are not interested in AT ALL?

I met a guy who asked for my #, and not wanting to be rude, I gave it to him. He texted me the next day, and I have yet to respond. Do I ignore it completely or drop the “boyfriend” line? I don’t actually have a boyfriend, but I think that would keep him away. I know that’s a bit immature, but I also feel like an uber direct “I am not into you” is not really called for in this situation. Not sure if it matters, but this was not the first time I met him, it was the second time we had run into each other.