Combination of velocity and oscillator. Used to describe a driver on the same road as you, usually a lonely highway. You're traveling at a constant rate of speed, but that other jerk will go a little faster than you, pass you, and you'll be rid of him...but then he decides he's going too fast and lets off on his gas...then his car slowly makes his way back to you, and you pass him...then he speeds up and passes you...and then slows down....and over and over again. Usually ends up with you flooring your accelerator and putting so much distance between you that he can never catch up. Usually an old person, or someone from up north whose mind doesn't work quite right.
Me, to wife: What the hell is that guy doing?
Me: That douche right there. I passed his slow ass two miles back and he's crept up on me...now he's passing me. Why does he keep changing speeds? He's a veloscillator!
Wife: Don't let it eat you up inside. Put some love in your heart.
Me: NOW what is he doing? He's slowed down and I have to look at his dumb face again!
Wife: Well, he's behind you now. You sure are handsome.
Me: Look at him! Now he's passing me! Is he in love with me? Is my profile that awesome??!?!
Wife: Well, actually it is. He might have a crush on you.
Me: LOOK AT THIS GUY! Now I've passed him....I'm so sick of this shit! VRRROOOOOMMM.....let's see this asshole catch me now!