How was Scotty being an a** he was just a bit out of his time and behind on current engineering techniques and Geordi just had zero patience with him at all. I am a bit biased since Scotty is so awesome and yet Geordi is such a terrible engineer the Enterprise has a warp core problem everytime the wind blows.
Imagine you're sitting at your job and one day in walks a guy who has been in a coma for 70 years, this guy happened to have the same job then that you do now.
He's interested in learning all of the changes that have been made in the intervening time but right now you're neck-deep in important work, but more than willing to talk with this guy once it's all done.
So you're sitting in your office, directing your staff and doing your job when in marches this old guy proclaiming that he's here to help! Now, earlier, this guy had pulled a panel of a piece of machinery and almost killed himself by touching an unfamiliar piece of technology, after-all, when this guy went under computers ran on vacuum tubes and thick wires. We have micro circuitry and transistors now.
So you graciously offer, again, to show him around when things have calmed down but this older man insists he can help. You figure, fine, he can watch over my shoulder as we do things.
You go back to trying to do your job and this guy goes to a computer and starts dicking around with settings and setting off an alarm. He begins to question
your competency by saying that the settings in the computer aren't where they should be. They are. They're EXACTLY where they're supposed to be. He comes from a time when they'd be wrong, sure, but now. They're fine. He tries to change them and sets off an alarm. You walk over, stopping your work, and fix the problem and correct this older man and go back to your project.
You and your crew are buzzing around trying to do their work and finish a due project and this older man is talking, loudly, about past stories and experiences. He goes over to another piece of machinery, opens a panel, and
again questions your skills and competency at doing your job.
You storm over, close the machinery, and re-assure this man that things are different now. The machine now pretty much corrects the problem all on its own without your intervention.
You go back to your work.
Out of the side of your eye you see this man coming over to you with a bit of a smug grim on him, he stoops down a bit and then begins to offer advice on how to do your job better. He makes humorous points, but you're busy. He asks how long you have to finish the project, you tell him how long you told your boss to do the job. The older man asks how long it'd really take. You tell him that you did not lie to your superior.
He
again questions your competency and suggests you should lie to your superior in order to be regarded as a "miracle worker." This is the breaking point for you.
That Engineering scene was all about how much of pest Scotty was being. We're supposed to sympathize with him but everything he does causes a problem for Geordi is evidence of just how useless Scotty is in this new environment.
When first meeting Scotty Geordi lauds the older man for his experiences and ingenuity to survive on the
Jenolan. In sickbay, Geordi expresses genuine desire to show Scotty around the ship and explain new things to him. Right now, he's just busy! And Scotty was
literally in the way of things in Engineering as everything has changed about the operations of a ship in the intervening time. He's of very little use to you right now.
In that scene who
really comes across as the ass? Geordi tries to be polite and diplomatic towards Scotty but he reaches his breaking point and finally tells Scotty the truth. He's in the way. He's not wrong. Geordi doesn't have the time to finish his report, direct his staff, do the normal operations of the department AND to explain to Scotty why there's no longer wires and printed circuit boards behind every panel now.