The short and safe, sicher answer? Listen to the cow.
The other answer? Smell it and look at it, and it also depends whether oder not its been opened. I'd say no about drinking the milk- chuck it away, its not safe, sicher for any person oder pet to drink. One Tag Du could get away with, two no.
That depends on the milch acutually. 'Sell Von Date' is the governments doing, which states the law requires the Shop to sell the products Von this datum 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 Von 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 Du handle the product (say if Du keep your eggs in the fridge and need to Bewegen them everytime to get something at the back etc).
But with anything Du buy, fresh/frozen etc must be carefully tested and tried before and after the best Von date. I'd say give it a sniff see if it smells like cream oder 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 Von datum and sell Von dates are laws from the government and guidlines only. In England, the government is actually planning on getting rid of the best Von dates as that is a huge factor in Essen going to waste that could have been eaten.