What are some signs that a therapist may have poor boundaries with their clients?

Off the top of my ancient head:

General Introduction to Boundaries from Panahi Counseling:

Serious disappointment when the client cancels a session.

What would you do if you were lost at sea in the Florida Keys?

Disclosing feelings, fantasies, and experiences to the client in ways not related to the work the client is engaged in.

Frequent phoning or texting of clients to “check up on them and make sure they’re OK.”

Struggling with fantasies of deeper connections with clients, whether sexual or parental or other intense or intimate relationships beyond psychotherapy.

What is the reason for writing X^2 as XX instead of X*X?

Obsessing about clients outside of work hours.

Eager anticipation (or anxious anticipation) of the next session in ways that distract.

Session-expressed curiosities about client details not relevant to the therapy.

Some men love anal sex more than vaginal sex. Why?

These items can happen fleetingly, briefly, in any therapy, but if they’re frequent, it’s definitely time for the therapist to get some good, solid supervision/consultation.

Sense of competition with persons who are important in the client’s life.

Routinely going over the time limit with certain patients, compromising the time for the next client.

What is the correct way to say "you're welcome" in French? Is it "de rien" or something else, and if so, what is it exactly (including accent marks)?

Failing to mention the client in supervision/consultation, out of fear the supervisor/consultant will advise return to ordinary healthy boundaries.