Uncultivated young man.
To be mashed on and to be spoony on are rather common expressions for to be in love with. (Cf. to be nuts on.)
According to Leland, the term mashed originates from the Gipsy-word mash = masher-ava: allure; according to others, it is a variation of smash[6]. (Smite, smitten is used in the same sense.)
In the eighties, it came to England from America, where it was used especially among actors.
Cf. mash: sweetheart. to mash, to be on the mash: to flirt. masher: (1) a species of Don Juan, esp. among choristers and actresses; (2) a dandy and, as adj., smart.
The term is, I suppose, originally actors’ slang.
slippy
»You make her marry the Prince; and be slippy about it.» (They And I. 75. 14.)
A schoolboy.