Why can't people speak English anymore?

Standing in the queue at the sandwich shop for my lunch I am assailed on all sides by young people calling out "Can I get .... such and such?". "Can I get?" - what sort of language is that? Of course they can't get anything - it is not a self-service establishment. They have to wait in the queue to be served like everyone else. With the huge variety of ethnic minorities now living and working in this country and struggling to learn the language, the least we thoroughbred English can do is to speak the language properly so they can easily pick it up. What chance have they got when all they hear is some warped version of the mother tongue such as "Can I get?".