AFL
Collingwood 1970 Grand Final: Depending on which side you are on, one of the greatest Grand Finals of all time or one of the darkest days of the 20th century. Collingwood gunning for its first since 1958, were up by 42 points at half time and seemingly unstoppable. But what happened next scarred many Magpie fans for life, and was used to strike the fear of God into young Pie supporters for years to come. Carlton kicked 13 goals to four to win by 10 points, with Alex Jesaulenko taking that mark. It also gave birth to the "Colliwobbles" which haunted Collingwood until 1990.
Port Adelaide 2001 - 2003: The AFL's youngest team made a huge splash when it played off in a Qualifying Final against the Brisbane Lions in just its fifth season. Their loss in that game, and the follow up loss the the Hawks a week later (despite leading by 17 points into the last quarter) was no disgrace. Just a young team finding their way they said. But subsequent losses in '02 and '03 where they failed t:o make the Grand Final despite finishing on top of the ladder warranted the public labelling them the Port Adelaide Chokers. This branding led their coach to make this gesture after winning the flag, ironically just a year after they were named chokers.
Richmond 2012: It just wouldn't be a list of meltdowns without the Tigers, who have been the providers of equal amounts of mirth and despair since they last tasted premiership success in 1980. But their effort against the winless Gold Coast was one right out of the box. Less than thirty seconds to play, 10 points up only Richmond could find a way to lose that.
Special Mention - Michael Rischitelli: As commentator Anthony Hudson once said, "I see it but I don't believe it."