Dining Etiquette -Licking the fingers:
Introduction: Amongst the laws associated with eating, and the proper blessing that should be said before and afterwards, are also laws relating to eating etiquette or table manners. The Torah directs us that our eating is to be done in a polite and respectful format, befitting of respectful individuals, and one should not debase himself while eating to act like an unmannered and low-class individual.
The law: Amongst the laws of table manners is recorded that one should not lick his fingers when he eats. Although eating with one’s hands is sometimes acceptable, by certain foods, nonetheless, one should not lick the food from his fingers, and is rather to use a napkin and the like to clean them. This certainly applies when eating with a fork and knife, and one just happened to get food on his fingers.
 Miseches Derech Eretz Zuta 5; Rokeiach 329; Reishis Chochmah Shaar Hanava 7:5; Elya Raba 170:23; Chesed Lealafim 170:5; Kaf Hachaim [Falagi] 22:63; Aruch Hashulchan 170:7; Ben Ish Chaiy Behar 1:9; Kaf Hachaim 170:72; Ketzos Hashulchan 39:3; Piskeiy Teshuvos 170:14
 See Nedarim 49b; Shelah Shaar Haosiyos Kuf