Difficult to be worse than many of the characters mentioned so far, but I’ll go with Francis Begbie from Trainspotting novels as he hasn’t been mentioned yet. He’s a psychopath prone to spontaneous violence and manipulating his ‘friends’ to his will. Ghastly fellow.

It’s been a while since I read Marabou Stork Nightmares, but I just skimmed through the Kindle edition and the language is generally straightforward throughout. However, some of the dialogue is in Scots slang, though it doesn’t look to be as prevalent as in e.g. Trainspotting.

I think you’d be fine with it, though I would recommend some of Irvine Welsh’s more popular books first, if you’ve not read them. Trainspotting, Porno, Filth, Glue are better IMO… they do have more Scots slang in them though.