Deal or No Deal/Funny

Even Luck Based Missions can be hilarious if something goes awry.

America

The PC game allowed players to replace the default amounts with their own amounts...or even custom prizes. This video shows the extent of that, with a year's supply of calendars, a Hannah Montana poster, and a 1971 Pinto.
In one episode, they had a contestant's sister replace one of the models. The contestant completely failed to recognize her, causing Howie to drop increasingly blatant hints.
One episode had a contestant a bit too excited, causing her wild flailing to knock over the phone and breaking it! Luckily, they had a replacement after the commercial break. The banker then docked $10 off the next offer to pay for the phone.
One female contestant was shown a lemon on wheels, then told the deal was "what's behind that". The player, looking at him with a serious face and arms crossed, replied with "...the girl?"

August 25, 2009: In Des' game, one of the players-in-waiting had a bit of trouble with Box 17 and ended up tilting the box back instead of opening the lid. It doesn't seem like much in print, but pretty much the entire Dream Factory couldn't stop laughing.
David's game had him pick Box 2. When the box was opened, there was no amount inside — only four pieces of black sticky tape. He was given a choice — either restart his game, or have the remaining thirteen amounts (including the one that was supposed to be in Box 2) shuffled and continue his game from there. David chose the latter, and found out that Box 2 was supposed to contain £250,000.
Nikki's game was an odd one as well — she got no offers above £250, and managed to get offers as low as 6p.
...But that's nothing compared to this guy, who got offers of £1, 10p, and 1p.