The dollar has been a trusted currency and is used universally. It is not easy to discount a currency that has built a lot of trust all over the world.
It would not be easy for it to go down but if things go on as is, it is very likely that it will become less valuable. It can lose value real fast like what happened to other currencies in the past that has been long forgotten.
I wonder why people becomes FOMO because of this man tweets

people get into this FOMO because they personally believe bitcoin itself, like gold or any other commodity, can be a safe haven for the speculated upcoming economic crisis of US.