For those noobs who don't know who John McAfee is:
1. John McAfee is the person who promoted scam projects such as SimmitriToken and Zombie Coin
2. He charged ~20% of the total supply of the ICO, in exchange for the promotion
3. In other cases, he charged $105,000 for each tweet he made to promote the scam ICOs
4. He is suspected of involvement of the murder of Gregory Faull in Belize
5. McAfee fled to Guatemala, in order to avoid arrest by Belizean authorities
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I read most of these. If you permit, I'd like to add this to the OP.
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I really forgot, this is one of the reasons why he is called a clown. He posted the tweet to spread FUD, because as we all know, he has been paid several times to praise a project regardless of the conditions that occur. Although honestly I hope that prediction will come true because I have converted most of my portfolio to bitcoin at that time.
As discussed in the previous comments, McAffee did say some things against bitcoin but he made that particular tweet to spread FOMO though.