I have two that come to mind...Ice Age 3 and Madagascar Kartz. Both are very easy games with VERY high completion rates but both of them frustrated me to no end. With Ice Age it was one of the time trial deals where you're standing on a snowball rolling around. With Madagascar Kartz it was the same thing, for the most part...time trials. I spent more time yelling at the cheap ass AI in MK than I did playing through Kane and Lynch 2 on extreme!
Obviously I could have kept both games a little longer (had both from Gamefly) and just continually tried until I got them but my patience just wasn't that stout.
I have no problem admitting it when a game kicks my butt, even a family/kids game, since I can always fall back on the excuse that I'm old and slow
So...if you can talk yourself into admitting it in public, what's yours?