Can a high PR, or any PR for that matter, backlink from an unrelated site hurt my ranking on search results?
It shouldn't do but who know with G. It might hurt your pocket and it is unrelated and has no impact on serps
It can't do anything to you, if it did I would to it on my competition, the only thing that can hurt you is outgoing links from your site.
Links for non related sites are usually ignored so no it's won;t harm your site. Google realises that anyone can post a link to your site, so they won't penalise you for inbound links, it's only outbound links to spamming sites that they will penalise you for.