To be fair, what people find weird or not about bus enthusiasm isn't the same as etiquette. As long as people aren't inconveniencing or offending others, putting themselves or others in danger or breaking the law, then who gives a monkeys? If someone wants to fixate on the B7RLEs of Lothian....well, it's not my preference but so be it.
Where this thread came from is about etiquette.
It's those people who do inconvenience or offend others, put themselves or others in danger, or who break the law.
It's those enthusiasts who offend owners of preserved buses by inviting themselves onto a bus (when doors are closed or signage says otherwise) and drop litter or clamber in a cab. It's those who offend owners by advising them that despite the many thousands they've spent, they've got it wrong (and yes, I appreciate some people don't get social cues and don't realise their well meaning advice is rather insulting). Or simply offending others by not using cleaning products on themselves or their clothes! (One personal one are those people who post BS - either because they maliciously post rubbish, can't distinguish reality from imagination, or simply guess - if 1035 and 1039 are moving firms, then 1036 to 1038 simply MUST be moving too?).
It's those enthusiasts who have to get THAT photo. That means berating others at rallies because they've spoilt the shot. It's running across busy streets or bus stations and putting themselves in danger and distracting the driver; the latter point also covered by using the flash.
It's those enthusiasts who enter bus depots and wander round putting themselves in danger, wandering into pits etc. Worse still, thieving mementos of their visit.
If you don't do those things and want to spend your time cataloguing your 1980s Ribble Almex tickets or getting a sexual frisson from a 1967 Chester Guy Arab (or even an Arab Guy called Chester), then so be it. It's not for me but it's a big world with many worse things in it.