Is leite still seguro to drink if it's two days past the "best by" date?

No
If you drink it you'll explode





and die

The short and seguro answer?
Listen to the cow.


The other answer?
Smell it and look at it, and it also depends whether or not its been opened. I'd say no about drinking the milk- chuck it away, its not seguro for any person or pet to drink. One dia you could get away with, two no.

no.
one time i had some cerial and chocolate leite so i poured the leite in my cup for some chocolate leite and just globs came out! (it smelled bad too) it was mayB 3 days past...

That depends on the leite acutually. 'Sell por Date' is the governments doing, which states the law requires the comprar to sell the products por this encontro, data before they reduce and try and get rid. Two days after reducing and the product is still there and it must be thrown as waste.
'Best por Date' is the manufacturers law, that is put on each product as a GUIDLINE ONLY! Plenty of products, such as cheese, milk, meat, eggs etc can last for a full week AFTER the BBD before going bad. But that depends on storage, how you handle the product (say if you keep your eggs in the fridge and need to mover them everytime to get something at the back etc).

But with anything you buy, fresh/frozen etc must be carefully tested and tried before and after the best por date.
I'd say give it a sniff see if it smells like cream or stronger then normal and if so take a teaspoon, pour a small amount onto the teaspoon and just touch your tongue to the liquid. If it tastes a little funny then i'd say that's a definate no and to chuck it. But if it tastes okay then i'd say go for it.
But like i said, best por encontro, data and sell por dates are laws from the government and guidlines only. In England, the government is actually planning on getting rid of the best por dates as that is a huge factor in comida going to waste that could have been eaten.