There are two things that I will never joke at someone's expense about. (There are generally more than two, but these two are nolle prosequi material.)
1. A person's name. Even Drumpf. (Perhaps especially Drumpf; after all, it's not like you need to go excavating the ancestral past to find criticisms of that guy.)
No matter how unique you think your humour is, I guarantee you: the person has heard that joke before. Dozens of times. Maybe they even still give you a pity-laugh to stifle the sound of their eyes rolling.
2. What Bertie Wooster would call a person's "outer crust." Unless it's something foreign, like crumbs or something (which, you'll note, people never mention, and just leave you to discover it hours later in the mirror. Thanks.), you can rest assured that a person is much more intimately aware of what is on display than you are. There's simply no tact or sense in pointing out someone's unibrow, mole, acne, tendency to turn deep vermilion when embarrassed or just after the dreaded 20-minute-run PE class, birthmarks... the list goes on. I include tattoos in this, if the comment comes from a total stranger who would otherwise comment on the weather. For everything on this list, they know about it. They know you can see it. No need to verbalize.
There's something private about a person's body—even the visible parts—that merits respect.