Some argue that Model Rule 8.4(g) contains language that leaves room for ambiguity.
The Comments (3-5) to Model Rule 8.4(g) provide detail regarding discrimination, harassment, conduct related to the practice of law, and activity that would not constitute misconduct under the Model Rule.
“Proposed new Comment  also explains, ‘The substantive law of antidiscrimination and anti-harassment statutes and case law may guide application of paragraph (g).’ This provision makes clear that the substantive law on antidiscrimination and anti-harassment is not necessarily dispositive in the disciplinary context. Thus, conduct that has a discriminatory impact alone, while possibly dispositive elsewhere, would not necessarily result in discipline under new Rule 8.4(g). But, substantive law regarding discrimination and harassment can also guide a lawyer’s conduct. As the Preamble to the Model Rules explains, ‘A lawyer’s conduct should conform to the requirements of the law, both in professional service to clients and in the lawyer’s business and personal affairs.’” (ABA Report to the House of Delegates, Page 7 of Report.)
“Some commenters expressed concern that the phrase, ‘conduct related to the practice of law,’ is vague. …The phrase ‘conduct related to’ is elucidated in the proposed new Comments and is consistent with other terms and phrases used in the Rules that have been upheld against vagueness challenges. … The proposed scope of Rule 8.4(g) is similar to the scope of existing antidiscrimination provisions in many states.” (ABA Report to the House of Delegates, Page 9 of Report; See footnote 22 on Page 9 for existing state examples.)