None of these uses is "slang", which is language (typically words and phrases rather than syntactical constructions) currently fashionable among a relatively small speech community (typically young people).
We entertainers for "We are entertainers" is dialect, African-American Vernacular.
You mad for "Are you mad" is a sort of ellipsis called 'conversational deletion', described here, and is common in all varieties of spoken English.
Don't ... ? for "Doesn't ..." is non-standard but very common in the language of those who are indifferent to standard usage. The underlying construction here, abbreviated by conversational deletion, is They [= "there"] don't {anyone/anybody/nobody} VERB, equivalent to There isn't anyone who VERBs. This is a non-standard idiom common only in American English.
2, conversational deletion, is acceptable in informal conversation; the linked Answer on ELU describes its construction.
But I advise you not to emulate 1 or 3: 1 will be taken either as mockery or as an illegitimate claim to membership of the African-American speech community, and 3, unless employed ironically, is generally regarded as a mark of uneducated speech.
