An exclamation from Harry Potter which is similar to "Oh Lord!"
"He just shat his pants!!"

"Merlin's Beard!!!"
by Merlin Himself May 26, 2009
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A layer of semen on a girl's face in areas where facial hair is commonly found on men, e.g. chin, upper lip, cheeks, neck. Usually results after a blowjob.
"Do you want a blowjob, sweetheart?"

"Yeah! How do you want it to end today, honey?"

"I'd love to have a Merlin's Beard, but whatever you want. It's your special day."

"You want it, you got it!"
by Merlin's Wife July 2, 2009
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When having sex with a young lady one withdraws his love staff at the point of ejaculation and sprays his love muck on the lady's chin. The jizz should start to hang down off the chin, creating a rather fetching white beard look, similar to Merlin's.
"Hey guess what Rich, I did a Merlin's beard on your mum last night!"

"Oh right I just thought she hadn't shaved!"
by Ste Crayston December 5, 2006
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Where one ejaculates onto one's partners face, leaving them with a beard dripping from their chin
1.

Dave: I was with this girl last night.
Tim: Oh yeah, how'd it go?
Dave: Got a blowjob
Tim: Did she swallow?
Dave: no, mate she likes it with a Merlins Beard
Tim: ......
Dave: Yeah....

2.

Steve: Want me to pull out?
Daisy: yeah, give me a Merlins Beard
by Jimmy Buttcracker August 17, 2013
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