To "do a Colin" is a synonym for any broken promise/lie.

Spawned from the twitter trend #IamColin. In reference to twitter user @cwarr07 who promised to donate 100 pounds to a cancer charity if he lost a bet. He lost and refused to pay. This started a twitter trend where people have been donating on his behalf to the Sir Bobby Robson Foundation raising almost 1000 pounds.
John: "Fred promised to help me with moving house last week. On the day he never showed up or answered his phone."

Terry: "Fuck him, he's always Doing a Colin"
by toonarmymia July 29, 2011
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To intentionally slur or defame someone under the pretext of being a friend.

To shit-stir because you can.
Why is Fred so pissed off?
Oh, Sandra is Doing a "Colin" and telling him everyone hates his new haircut.
by The Master of Disaster! January 19, 2015
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