Would you americans fucking relax about it?
It's just a stupid chant that originated from the hit "Whoomp There It Is" by Tag Team.
That song was a huge hit worldwide and in Brazil as well, so some soccer fans started to chant UH TERERÊ after goals, which is phonetically what "Whoomp There It Is" sound to us brazilians.
There's still to this day some clubs which their fans chant that after each goal, as you can see here:
It got then changed in some contexts to "Uh, vai morrer", which just means you're gonna lose, we used to chant that in soccer tournaments in elementary school.
It's just a hyperbole, like you guys say for example "Khabib is a monster, if he fights that guy he's gonna kill him".
I'm brazilian and I don't even live in Brazil because of it's problems, but please stop acting like the crowds are wishing death on foreign fighters, EVERY SINGLE event in Brazil the commentary team brings it up like brazilians are a bunch of savages that would kill all the foreign fighters if the cage wasn't there.