Answer
Unjust vexation is punished under the second paragraph of Article 287 of the Revised Penal Code, which penalizes "any other coercions or unjust vexations." It is a catch-all offense for human conduct that, without violence, annoys, irritates, vexes, or disturbs another person without any lawful or just cause.
The gravamen — the heart of the offense — is the disturbance of the offended party's peace of mind. Because the article does not list specific acts, courts look at whether the act caused annoyance or vexation and whether there was a legitimate reason for it.
Sources & further reading
Research aid — not legal advice. Verify the current text against the Official Gazette. Provisions may have been amended or repealed. Using this page creates no attorney-client relationship. For legal advice, consult a Philippine lawyer.