Dogs who beg from or push at people for treats during meals do so because their annoying behavior previously earned tidbits.
TABLE FEEDING Corrective Actions: Everyone must stop handing the dog food while eating since even occasional rewards encourage incessant begging. If family members, such as children, tend to drop morsels of food on the floor during meals, confine your dog away from table to prevent accidental rewards that encourage continued begging. At first sign of begging, confine dog away from table. Never allow dog to lick dinnerware and clean up scraps left on tables after meals.
(Courtesy of Dogchannel.com)