Web author Twisted Hilarity's popular story The Last Pure Human features Max, who finds himself centuries in the future on an alien planet after being cryogenically frozen on his way to a colony, Exty Years from Now. To summarise, he finds himself unwillingly 'married' to giant alien Cat-Man Kasan: cue a long, long series of "I hate him. I'm not even gay. I am totally not into his huge hot body. I am not going to lead him on, especially not when he does that sexy smile of his. Nope. Not one bit." Thankfully this grows less prominent as the story goes on.
Gardevoir in Pokemon: World of Chaos. She is always mad at her master Tee-Jay, calling him "jerk" and stuff, partially due to the fact that she is a Shadow Pokemon (and a former Dark Pokemon), and so her heart is "closed". But she is very jealous when TJ speak to women and blushes everytime he made her a compliment.
David Chapman from you could make a life. He's convinced that he hates his rival Jake Lourdes, but when Jake asks him why exactly he hates him so much, the only response David can come up with is to kiss him. Add to that how his icy treatment of Jake begins giving way to blushes and shy replies when Jake doggedly keeps on pursuing him and how he has no experience whatsoever in dealing with feelings of love/attraction, and you have a bonafide tsundere on your hands.
Although that may actually be a subversion; she's not being "tsundere", she's just sick of them both and their ugly faces, not to mention this whole fruitless kidnapping/rescue thing.
Church from Red vs. Blue probably fits in here somewhere. He's a jerk most of the time, but on occasion shows that he really does care about the rest of his team (and about Tex). The instant he realizes that he's done so, however, back comes the tsuntsun side. Tex is just plain tsuntsun, though. It particularly shows up in this episode when Tex and Church confront O'Malley.
In season 8 his deredere side comes out a bit more. Then again, it's kind of maybe not quite the original Church.