I suspect it's a VERY local idiom, but "watching for subs (submarines)" was the local term for necking in my home town on Cape Cod. (Still is, according to relatives)The term for "soft Drinks" was split more along age lines then anything else... the oldest folk called it "tonic" - most of the adults called it "soda" - unless they were "newcomers" - who called it "pop" - and most of the youngers ones called it "coke"
'course I'm 25 years out of date now....
MMario