When you throw a McDonald's Shamrock Shake into a large crowd of people on St. Patty's day, resulting in a large crowd looking like it has been covered in a green semen. What might happen if a leprechaun skeets on 5th avenue in Manhattan.
1:"Watch this."
(throws shamrock shake into crowd)
2:"Oh my God. It looks like a leprechaun skeeted on them"
1:"That would be a St. Patty's Day Grenade."
by Mr. Charles McMeaty March 13, 2011
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A promise that every year on Saint Patrick's Day two or more friends will go on a walk while smoking a cigarette, even if they loathe one and other they must do this.

This is almost like a task to those who take the oath.
Friend:"Are you and -insert name- going to follow through with the St. Patty's Day Pact?"

Me:"We hate each other, but it has to be done."
by Mogan Bee March 18, 2007
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On my way back from break, i decided to roll a St. Patty's Day Fatty. On St. Patty's Day.
by Token Asian March 18, 2010
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