You don't have to be young even ; I am 54  with a BMI of 19.4 , and I have noticed an uptick in rude female cashiers  over the last year or three (AND an utter dearth of non fat cashiers, too). I think that fats on  tumblr/instagram/FB etc et al are encouraging each other to be hateful to non-monster customers.  FWIW, the rude  cashiers all seem to be under 30, possibly because they don't give a shit if they lose some crappy minimum wage job while older fats know they won;t get anything better and so can contain their urge to be hateful to the slim.