Euphamism for the all time, number one, undisputed solo male pastime.
Masturbation, in case subtlety's not your thing. Tommy tank. You know.
"Knit one purl one knit one purl- AND cast off..."
(Declamatory) "Did you see Gavin & Stacey last night?"
"No. I was knitting."
(Perjorative) : "You dirty little knitter !"
(Descriptive) *When a pretty girl (or boy- we must be inclusive here) walks into view* "Ah- a new pattern!"
(And if 'new pattern' has been particularly apposite:) "I blunted my piggin' needle last night. Dropped a stitch".