Yeah I do know Gers fans rather dislike Aberdeen. Incident with someone , was it Barry Ferguson's brother Ian I think? getting injured and the Aberdeen fans being rather nasty about it? As a Non Scottish Rangers supporter it's not fully in my bones as it would be yours. Still imagine their decidedly the lesser of two evils when paired with Celtic. Plus it can only be good for football in your country to not have a duopoly . That being said Rangers winning a few in a row ASAP will elicit no complaints form me
Ian Durrant (who was a fantastic young champions league level player at the time) was brutally, and deliberately injured by an Aberdeen player Neil Simpson, which resulted in Durrant never being the same player, and Dons fans enjoy singing about that. Add in that they are the third club in size, success and fanbase, then you have the second most hated team for a Gers fan.
The duopoly of course wasn't a bad thing for most of scottish football history, when Rangers Celtic and occasionally another team would do well/very well in Europe, but Rangers downfall in 2012 meant that scottish football was exposed by the fact it had basically one team worth of note capable of competing in europe and actually winning the league.
Put it this way, i would list the following in order of hatred (The gap between Celtic and the rest is deliberate, to show the distance)
Celtic
Aberdeen
Dundee United
Hibs
Hearts
Motherwell
I don't really think any fans of other clubs outside of Scotland really realise that Scottish Football and Scottish Society can be very poisonous and divided at times, much of it rooted in football, some of it in more serious issues such as independence. Even when English players come up they are not only astounded at the actual size of football clubs like Rangers and Celtic, they are taken aback by the hatred and bile in the scottish game. (I'm not hiding from the fact rangers should take their fair share of the blame)
The so called 'non-old firm clubs' absolutely despise the OF and their fans are despicable at times, and this is shown up to an executive level at these clubs. Obviously rangers and celtic have the longest rivalry and naturally despise one another, but it, and more so in the last 20 years, has become more obvious that the OF are utterly hated, and i would argue Rangers are hated considerably more than Celtic in Scotland, evidenced through the other 11 SPL club voting rangers to the third division despite being found not guilty of the big tax case.
However that's the blue glasses talking, i tend to enjoy seeing scotland in general doing well on the big stage and im a big advocate of Executive reconstruction in the scottish leagues to help clubs financially