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!"
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.
Where one ejaculates onto one's partners face, leaving them with a bearddripping 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