Originally created as a more elegant way of describing something shit. Jupptac is a derivative of the words "Gyp" as in gypsy/pikey/shitty/budget/pauper and "Tack" meaning tackle, but also used to describe stuff in general. Tacky stuff in particular. The word GYP-TACK was softened in pronunciation to become JUPPTAC.
Pronunciation - jjjjj-ooooop-tak
"a double vodka jupptac please barman" roughly translates to "a double shot of vodka in a glass mixed with any old shit you can be bothered to put in there" ie 54pence orangeade from down the happy shopper.