What did Laud Humphreys do that was considered unethical in his study of men who engage in sexual acts in public restrooms?

He disguised himself and did follow-up research on the men by pretending to be conducting a medical survey.

Explanation:

This research is known as Tearoom Trade.

What Laud Humphreys did was an act of voyeurism, which means observing others while they are involved in sexual acts, usually for one's own sexual gratification.

He would carry out this way of observing without the subjects' consent and even lied by not disclosing the true intentions of his research, amongst other things.