Stands for Smoking Blow Job. If you dont inhale on a cig properly you breath out thick, heavy smoke. If giving head when you do this you can use the thick smoke to make a blowjob more interesting and pretty.
A 'Nikola gave me an sbj last night, it fucking rocked!'
It means Definitely. Deffo is short hand for Definitely, just add a Jeffo for coolness!
Q 'You want to go to the movies?'
A 'Deffo Jeffo!'