Tolerance as defined by science is accepted amount of error, or expected error. As defined this way, bigotry would be defined as anything outside that range of tolerance. Given people and social normalcies vary so greatly, a numerical system cannot be implemented to judge the tolerance range of areas.
Needless to say the world grows more tolerant, and what was once tolerance in range now has become acceptance. Acceptance is a step past tolerance, in that what it is applied to is seen no longer as a potential problem. Acceptance is to take ideals you may not entirely understand yourself, and support them because it humanizes an individual.
Things that would not be tolerable:
➩ Outright phobia to transpersons, other gender identities, sexualities, religions, nationalities, race, ethnicity, etc in insulting, aggressive, or pseudoscientific manners. Everyone is a human being and must be treated with basic human civility at a minimum.
➩ Sexualizing an individual based on sex, gender, identity, religion, etc. as stated above.
➩ Indirect slander of a person for items stated prior. This would include ‘outing’ them to other individuals.
➩ Deliberate use of a name, pronoun, slur, or word a person finds offensive within reason. For all intents and purposes, acceptable pronouns are those found in a dictionary. All others you may suggest use of, and it is suggested you use.
➩ Intolerance of mistakes. To attack another for misuse of a pronoun accidentally, or a different name you used to go by, is unacceptable. This is not bigotry. People require adjustment periods and still may make mistakes. As humans do. Tolerance flows both directions.
➩ Forcing ideals on a person or ‘clarifying’ something to them forcefully. If they identify one way, that is who they are. Your opinion of that has no weight or validity to their inner self, and should be kept to oneself.
➩ Forcing religious or political ideals on another. Specifically mentioned to avoid conflict based on religion or political idealization. You may speak of these things.
➩ Claiming ‘freedom of speech’ to cover your bigotry. You may say what you want, at cost of consequences. There is no protection for speech that incites violence or hatred of a population.
➩ Grossly disgusting language regarding a person. Take your dirty talk to private, and be silent if they request you stop.
➩ Attacking ‘cis’ or ‘straight’ people for being such. They were born that way, as were we all, and they are also humans deserving of tolerance and acceptance.
➩ Baiting arguments.
➩ Asking what genitalia someone possesses.
Things that are acceptable:
➩ Asking nonpersonal questions in a professional, polite manner. Word them very carefully, and if you are concerned they may cause distress or be perceived as intolerant, enter the topic gently or not at all.
➩ Stating one’s identity and preferred pronouns.
➩ Asking for one’s preferred pronouns.
➩ Asking preferences. Best to do this privately unless the conversation swings that way.
In essence, use a good personal judgment. Common sense is not so common, and these ideas are in place to serve as a starting point.