Shaking the ketchup bottle is a euphemism for male masturbation. The metaphor comes from both the vigorous shaking motion applied to a ketchup bottle, and the "splooging" of ketchup when you've shaken it for long enough. Note: If what comes out is actually ketchup coloured, then you should very likely consult a doctor.
BRB - need to shake the ketchup bottle.

I was vigorously shaking the ketchup bottle last night.

I think I spent too long shaking the ketchup bottle - I'd ran out of ketchup by the time I was finished.

Shaking the ketchup bottle is a great way to pass the time.
by orangepony April 12, 2012
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Speaking to Sky News after the swearing in of new ministers, Australian Prime Minister Kevin Rudd rejected the view that not enough women were promoted.

"Fair shake of the sauce bottle, mate," he said. "If you were to compare what this Government has done in terms of the promotion of women of talent and ability compared with our predecessors, it's chalk and cheese."
by Sideshow? June 10, 2009
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Used to inform somebody that they’re taking more than their share or are engaged in some kind of unfair practice.
In June 2009, Australia's Prime Minister Kevin Rudd when persistently questioned by a reporter about how he'd arrived at a decision about the composition of his ministers, responded three times during an interview "Fair shake of the sauce bottle, mate." Critics thought he was trying too hard to use Australian slang to boost his popular appeal.
by vexnews June 16, 2009
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