The term 'Sinking-a-digit' is commonly used when referring to a technique of female masturbation.
In most cases, the finger is 'sunk' into the females vagina with the view of creating an orgasm. This technique can be used on oneself, or administered to a 'special friend'.
In some circles, 'Sinking-a-digit' can be used on or by men, however this depends on several different variables. Mostly, the male must enjoy arse-play!
Boy meets girl at the fair, boy falls for girl, they board the rollercoaster and boy begins 'sinking-a-digit' into his new special friend.
Fogey/fogy /fougi/ sl. (early 18C+, orig. Scot) old-fashioned, stuck-in-the mud.
Person with old fashioned ideas which he is unwilling to change: Come to the disco and stop being such an old fogey!
You think me an old fogeyand an old tory, his thoughtful voice said. I saw three generations since O’Connel’s time. I remember the famine. Do you know that the orange lodges agitated for repeal of the union twenty years before O’Connel did or before the prelates of your communion denounced him as a demagogue? You fenians forget some things. (James Joyce, Ulysses. Penguin Books,1992. p. 38)