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If the person is truly a friend, I would give my advice about the investment and simply decline the request. A friend would understand

Yeah... they should know it.

Call the police

Get them thrown into jail

Laugh at the mugshots 😾

Hahaha... I wish I can!!! Sometimes, they are just too annoying!!

These sort of things to me are pretty much friendship breakers in the person keeps pushing them, I would just gently say no and ask him to stop but if he keeps on going and escalating, I would give a warning to never bring up the topic again because it could damage our friendship and if he tries again, he clearly cares more about earning profits from his scam than your friendship so its pretty obvious what that next step would be! 

That’s true... I had a few friends and relatives that I kept a distance from them now.

Sadly enough I had also a few encounters with friends approaching me with MLM. They are trying to convince you with a short coffee or something just to present their concept and their beliefs. I think you have to have a strong mind and personality to just say no. Personally I wouldn't want to have to get involved into a discussion. Just be friendly and polite - do not try to change them, because you will only run on ice with this. 

Yeah... that’s true. Strong mind is important.