Yeah, you'll see a lot of those kinds of pitches. I guarantee you there'll be at least one per episode. Sometimes there are some good ideas with bad pitches, where sometimes they get completely shut out. You'll sometimes see the hearts of the investors go out for these people if they like the idea enough. But sometimes the pitch is so bad and the pitcher simply hasn't prepared very well. In this case, you'll often seen the dragons/sharks berate them for not doing proper research and wasting their time.
Then there's the odd time when someone will actually pitch something that's already been done. I kind of feel for those people, because if the idea's already been done, then it's likely a good idea. There was actually one time recently where someone pitched a product to the Dragons that turned out to be very similar to something that had already been pitched to them, and the dragons told them that, but surprisingly instead of turning them down, one of them went for it, essentially becoming a competitor to the previous product/investor, and they were in that same room...
Dragon's Den here has been successful and long-running now, It was in its 4th or 5th season, I think, when the Shark Tank in the US started, and next season will be its 12th.. Since then we've had a lot of special episodes such as family episodes in which whole families appear to pitch their businesses, student episodes, second chance episodes in which previous unsuccessful inventors try again with different ideas to pitch, sometimes successful, sometimes not. There are also update episodes from time to time where they go back to previous investments or those that ended up getting backing through some other means and update the viewers on how they're doing with their businesses. So, it's a really interesting show that has a lot of merit.