While waiting in line at the grocery store, this dad and his 2-year-old son found themselves in the middle of a wild scene. Right in front of them, a Boomer was having a total meltdown over his apple juice, waving around a half-full gallon jug and loudly complaining to the poor cashier that it tasted awful. As the entitled Boomer went on and on, the toddler started to imitate him. Not quite old enough to speak, the kid still nailed the Boomer's whiny voice, causing nearby shoppers to stifle the…