Don't get me wrong, I hated Karofsky for a long while there. Then he did the unexpected (because I wasn't in the habit of reading Glee spoilers at that time): one day, instead of punching Kurt, he kissed him. And with that one incredibly complicated act and the subsequent ones, he became not just a random jock with slushies, but an equally complicated character. Someone who, unlike Kurt, was running in circles that weren't going to accept him as who he really is.
Dave (because I'm using his first name since Kurt does too) has been shown in so many new lights since he kissed Kurt: someone who not only enjoys dancing, but is good at it; a scared kid beneath the tough guy exterior; a good student (seriously, even I didn't take Calculus 'cause it's hard). With the Bully Whips (bring back the beret!), he got to use his anger and frustration against actual bullies instead of someone who reminded him how life could be aka Kurt and his friends.
Also, can we give it up for Max Adler? In a show that takes over-dramatic to a new level (and entertainingly so, don't get me wrong), his subtle changes of expression give Dave Karofsky a quiet nuance. I refer the reader to the scene between Dave and Kurt outside the classroom in the episode 'Prom Queen'. Actually I just refer you to the whole of that episode. I feel like there should be an award for Best Acting in a Certain Episode of a Show You're Sorta In just so I could present it to Max (at which point I would dissolve into giggles and blush)
Now, the reason I think Dave and Kurt should be a couple. Let's take a look at Kurt's present boyfriend, Blaine *insert Pretty in Pink quote here*. I don't really have a problem with the character of Blaine in general. Although he does make some funny faces when he sings and dances, but if i can overlook it for John Mayer, I can do the same for Darren Criss who is a great singer. In a recent episode, Blaine was given the chance to audition for the male lead in the school musical: the role Kurt is also trying out for. I also refer to basically Kurt's entire tenure at Dalton, where Blaine sang the leads and Kurt did back-up. Therein lies my problem with this couple: they clash. Not vocally, they sing beautifully together. I mean, this is going to be a problem in their relationship (not a spoiler, just a well-educated guess). The fact they're both so damn talented that it will always be one or the other who gets the lead.
Enter Karofsky. He has not been shown to have any singing talent up to this point (though if you look up Max Alder singing "New York, New York" you will not be disappointed). If Kurt were to get with him, they wouldn't be competing. And I honestly think each boy would be good for the other. Dave would calm Kurt down a little bit, Kurt would let Dave shine a little more (more Karofsky dancing!). Now I know this is just one girl's opinion, but yeah, I really think Karofsky and Kurt should become a couple. (also they'd be superhot together!)