"one for his knob"

aha! a 'cribdegreen'... [but check out the purported inventor's name!]

the jack in the suit of the up-card was called Noddy, or His Nobs
(fifteen-two, fifteen-four, a pair for six and one for His Nobs)

http://members.home.net/willoworks/cribbage.htm

[*almost 50 years of cribbage]

p.s. - the Mavens have another good entry today (12/08) on mishearing, etc.
http://www.randomhouse.com/wotd/

p.p.s. - we used to call His Nobs "nubbins" [this postscript brought to you by the Eternal Golden Braid, or Strange Loops Unlimited]