Refers to someone acting in a really pompous, overbearing way, arrogant without any reason to be so, acting a fool or a jerk; the implication is someone trying to act way above their "station" or "caste", having "jumped-up" where they don't belong. Usually accompanied by an insulting noun. A term favoured by Gordon Ramsey on his cooking programmes.
"You jumped-up little berk! You fucking gobshite! Who the hell do you think you're talking to? You're talking out yer arse, you know that, don't you"?
Over inflated ego showing arrogance. Not someone with people skills.
That jumped-up arrogant tool Spencer has no people skills.