Dropping a hint is like scraping ice off of your windshield; both are equally annoying, in both situations you'd give your least favorite grandmother for someone else to do it, and while you do both you long for a Utopia where we ride dinosaurs instead of cars.
This is an easy maneuver for a guy. Step 1: delete the girl's phone number from your cell phone. Step 2: set phone down on something that is not a sink or a toilet. Step 3: take a nap. If a guy is not interested all we have to do is stop calling and girls seem to take the hint pretty quickly.
Even if a guy hangs out with that particular girl again, a girl has this uncanny and mind-boggling ability to sniff out an uninterested guy. A theory of mine is that the sense is somehow related to the sense a girl has to be able to tell if a guy is in a relationship.
This one time I executed a flawless "No Call" and then followed it up with a "This isn't awkward" hangout session with the girl and a few friends. I didn't flirt, I kept all conversations casual and when I wound up drunk that night I made sure I was surrounded by a cocoon of friends to fend her off.
These defensive tactics dropped the hint pretty effectively, although I should mention that somewhere in the middle of that night I was slapped by the girl.
For a girl to drop the hint, it takes a little more effort because a girl is not only dealing with a guy's brain but also the tiny brain inside of his penis. You can start off by putting an away message up every time the guy signs online. Follow this up by making the away message a slew of obscenities directed at the guy you're avoiding. From there, stop answering his calls.
When the guy finally tracks you down like the cold-hearted harpy that you most certainly are, give him a one to two minute explanation of how things aren't working out. Punctuate the experience with either the middle finger or spitting into his face.
Why not just explain things first, you ask? Simple: a guy will assume you're playing hard to get. The combination off all of these "Ice Queen" tactics should get the point across.
Feel free to add your own touch to this process. Maybe you could spread some embarrassing rumors about the guy's sexual escapades. A message on his car written in urine would catch his attention pretty quickly. If he's REALLY not getting the hints then as a last resort you could try sleeping with his friends/brothers/sisters/father/grandfather and see how he feels about that. Actually, if you hit a few of the people on that list you should be in good shape.
Just remember that if you avoid the hint dropping, you'll just end up in a relationship with a partner that will probably demand an absurd amount of either sex or cuddling and when you detest the other person, one of those will weigh on your ability to not become a murderer.