Which behavior would raise a substantial question regarding a lawyer's honesty?

Engaging in fraudulent activities would raise a substantial question regarding a lawyer's honesty because fraud inherently involves deceit, misrepresentation, or dishonesty for personal gain at the expense of others. The Model Rules of Professional Conduct emphasize the importance of maintaining integrity and honesty in all aspects of a lawyer's practice. Fraudulent behavior directly undermines the trust that the legal profession relies upon, and any engagement in such conduct would reflect poorly on the lawyer's character and ethical standards.

In contrast, overlooking a minor procedural error is often viewed as a part of the complexities of legal practice and may not indicate a lack of honesty. Failure to report disciplinary actions, while indicative of a potential issue, does not necessarily equate to dishonesty unless the attorney is actively concealing pertinent information. Disagreements with clients are also a normal part of legal practice and do not imply dishonesty; rather, they indicate differing opinions or approaches to legal matters. Thus, engaging in fraudulent activities is the clearest indicator of a lack of honesty among the choices provided.