Ah, well, see, Rodney started off on SG-1... er, as jerk, I admit, but he was funny and weirdly obsessive, and he had a crush on Sam, which she found repugnant, as you might imagine. Umm. Why do I like Rodney? Why do I like Rodney? Well, the interplay between him and just about everyone makes me laugh. And the combination of smart, tactless, insecure, often right, not that brave, but reluctantly heroic when pressed works for me. I think he's just got a vibe that I enjoy, which I get does not work for everyone. In fact, I remember my early posts about Atlantis always having the caveat, "...but I'm worried his schtick will get old for me." But, you know, it just hasn't yet. So, there you have it. (But, I mean, the guy is a pain in the ass. I wouldn't argue otherwise. I just find him to be an entertaining pain in the ass.)
OK, I just thought of one scene early on that endeared Rodney and Sheppard to me. Have you seen the ep where Rodney gets the Ancient device stuck to him? There's an adorable scene in it when he and Sheppard have just discovered the wonders of the device, and Weir sort of boggles at how they decided to test it... and they're like two kids with the coolest new toy ever.
Also? I adore the Czech doctor. They're a hoot together, too.
And, I completely agree that sometimes Sheppard is smug. It bugged me a bit at first, but I think he's won me over with endearing more often than not, so I ignore.