Minor point incidentally, but they hate it when people call them Notts Forest. It's Notts County and Nottingham Forest. You might say that's a good reason for winding them up.
But I sort of understand them — for years it used to drive me round the bend when French journalists on radio and television would lazily talk about “Manchester” when they meant United! That of course filtered down to ordinary followers of football who knew no better. Now they've just changed camp with their laziness — we're “Manchester”! (Which is true, actually, but since absolutely nobody refers to either club like that, least of all their/our supporters, it's sheer ignorance).
It's lazy but the term just Manchester started for the rags as just a horrible extremely idiotic throwback, one to how teams were presented in the earliest European competitions it quickly became outdated. Sadly due to our demise and as we became more and more obscure in Europe for a quarter of a century Manchester stuck more with them, teams would generally at least 90% of the time for a decade be presented as the city where they're from.
As the rags won the European Cup when we were champions to avoid confusion we were immediately Manchester City in Europe, by then the practice of naming you the city where you're from had become mostly outdated, UEFA realised they needed to stop this as most major cities had at least 2 major sides so this only confused most.
The biggest confusion came towards in Portugal where Benfica's full name is actually SLB means Sporting Lisbon Benfica, they used to be but called Lisbon in the very earliest editions when they were champions, when really their fans just preferred Benfica so being referred to as Lisbon really annoyed them. Then when Sporting CP (Sporting Club/e de Portugal) got popular people kept referring to them as Sporting Lisbon due to this stupid naming where they're from, while people started calling Benfica the shortened preferred name of their fanbase, instead of Sporting Lisbon Benfica UEFA just shortened it to Benfica while calling Sporting CP the horrible Sporting Lisbon.
You can imagine how pissed off Sporting CP fans got when people around the world referred to them as Sporting Lisbon and not just for a while but over 50 years, rather than very simply the simple shortened term Sporting CP or Sporting Club de Portugal, they were being called the name of their most hated rivals proper name in their eyes.
The same happened in all the very earliest EC editions, wherever a team was from that's there name like Real Madrid were mostly called Madrid, AJAX Amsterdam (name at the time) became just Amsterdam to their fans annoyance, back when Athletic Bilbao was absolutely massive and qualified they went by Bilbao, Partizan Belgrade just Belgrade etc. even the rags weren't too happy initially as just Manchester most teams hated their localised name.
1860/TSV Munich fans weren't happy at being called just Munich as it ignored their full name, they were even more unhappy later when Bayern were called just Munich too at times despite being from Bavaria as in not Munich proper in their eyes.
For the sky blue team in Munich they hated it and despise the German rags makes you wonder why our teams fans aren't a little bit closer, if it wasn't for how badly German's are brainwashed on owners they'd make a great CFG team, sack it let's buy TSV/1860 Munich and make them competitive as that'd really boil Bayern's and their media's piss.