TL,DR General principle: If someone is choosing to do something and choosing to share / promote it, and it's not detrimental to them, it could be okay to joke about / pisstake / criticise. BUT If it's something outside their choice / control, that they're not actively sharing / promoting, and the thing could be detrimental to them, it's probably not okay to joke about / pisstake / criticise.
Possibly fair game for humorous banter or serious criticism:
1. Anything that is within a person's control or choice, that is not detrimental to them as a person nor in their climbing, and that they are actively choosing to discuss / share / promote. E.g.
Opinions in arguments
Principles / stances / positions on issues
Choice of media tastes if shared publically
Choice of other interests if shared publically
Behaviour or misbehaviour in the climbing arena
Anything that is deliberately and publicly shown off and promoted by a person, that isn't off-limits as below.
E.g. it can be fine to joke about / pisstake / criticise someone for their defence of climbing ethical principles, their argumentative / belligerent nature, their promotion / highlighting of obscure forms of climbing, their defence of UKB threads, their extreme music taste (if they promote it), their geeky / nerdy hobbies (if they promote them), their choice of problems / routes and maybe fashion sense in their videos / photos, their tendency to draw penises in the dust on mate's cars, etc.
(Obviously it's equally important to take into account what the target might feel and in particular if they clearly express they're upset by something e.g. "Yes I post loads of videos with a death metal soundtrack, but I don't like people joking about me being a greasy old headbanger who won't get any video views" or "I know I argue vehemently against headpointing, but I think it's unfair for people accuse me of being elitist and dictatorial")
Probably off-limits for banter / criticism, and tending towards bullying:
Anything that is
1. Outside of a person's control or choice.
2. Possibly detrimental to that person, and in particular detrimental to them in the climbing arena.
3. Something that they generally keep out of arguments / discussions / self-promotion and don't highlight publically.
4. Possibly something that is commonly regarded as undesirable or unpleasant. E.g.
Physical appearance
Body composition
Race
Gender
Sexuality
Accent
Family situation
Relationship
Social situation / status
Disabilities
Injury problems
Mental health issues
Neurodivergence
Being at a lower standard in climbing
Having suffered unpleasant circumstances
E.g. it's not okay to joke about / pisstake / criticise someone for being bald, having acne, being fat, being of mixed race, having been a victim of prejudice, being gender weird, being non-binary, their age, going through a divorce, stammering, having missing teeth, having poor posture, having long covid, struggling with childcare, success or failure of investments, obsessive tendencies, body image issues, having clinical addictions, etc.
(Obviously this is for general online / casual interactions, and things can be quite different between trusted friends, and/or when someone has indicated they're fine with the subject matter)
N.B. Obviously just my opinion suggestions but I think the distinction is pretty logical.