I'm going to point out my friend's blackheads
Why would you point that out to your friend?
It's fun to poke fun at people without their consent.
I think that sounds really cruel. It is not fine to poke fun at peoples' appearances. That is a very mean thing to do, and your friend will probably be offended and hurt. If you value their friendship, you will reconsider speaking so unkindly.
But I just have to say something like, \"Dude you got a blackhead on your nose\".
You shouldn't make fun of your friend based on their appearance and how their skin looks. I don't think you would appreciate it if your friend made fun of you.