Its a sex move. When the guy is about to ejaculate, he pulls out his dick, lays it on top of the chicks stomach, and punches down on his dick like a hammer when he is busting.

Seed is spread all over the place, just not watermelon seed.
"Dude, she is totally easy, you could for sure give her The Gallagher tonight!"
by CaliBoy Twizzler October 25, 2009
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1. extremely nice guy; sensitive

2. horndog; eager for sexual intercourse

3. amazing in bed; hot

4. extremely hilarious; will make anyone laugh
That really nice horndog is a gallagher.
by gallagher14 February 20, 2009
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After ejaculating on a girls buttocks, the man takes his penis, and much like a hammer to a watermelon, uses the head of his penis to splatter his own pool of semen all over her.
Getting inspiration from the prop comic, Ted decided to give his girlfriend a gallagher, unknowingly hitting her cat who was in the splash zone.
by ComediaAGoGo August 3, 2010
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(n.) a person or thing that acts in a manner such as imposing odd characteristics. Not normal.
"gallagher" a person saying odd comments like gub gub incessantly
by Dr. Jason Smith Ph.D UAP February 22, 2011
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A ginger guy who's into back alley gay orgies
I hate going down that alley, so many Gallagher's there
by Lawrence Smith May 23, 2008
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