What are "entitled Millennial whippersnappers"?

The definition of "whippersnapper" is "a young and inexperienced person considered to be presumptuous or overconfident."  It's an old fashioned term.  The word "millennial" refers to young people born in the 21st century and and word "entitled" means to feel you have a right to something.

So, the term refers to young people who think they know everything and believe they have a right to whatever they want.

It means spoiled bloody brats from the turn of this bleedin' century onwards, who think this poxy world owes 'em a bloody living. 

Geezerspeak for anyone under 30.