I was referring to the third party example, where there is an "imminent breach to the peace." The point about indecency can stand as it is: not how I'd order a society, but I get it.

However, I should not suddenly be in MORE trouble for wearing an indecent shirt because it made someone standing around me angry enough to get rowdy.

Public decency is not addressed by Section 5 of the Public Order Act, which was the act the police officer cited.