Often thought to be short for "You Bastard". it actually comes from the Gaelic war cry ‘aigh bas’ which means ‘battle and die’
made popular by the glasgow tongs, a violent gang in Scotland during the 1960s
Tongs Ya Bass!
Scots- "ya bass" is a shortened term of "you bastard" said by many Glaswegians usually in an aggressive tone.
"mon ya bass, i'll fuckin' do you!"