backslap

verb

Etymology: From back + slap.

1. To enthusiastically affirm or congratulate a person, especially by patting them on the back.

   “In public he put on a performance that was at once outraged and outrageous, but usually he did not carry grudges into his private life. Exuding the backslapping air of a socializer who loved to gamble and drink, he could not understand why people whose careers he had ruined and publicly ridiculed would be hostile to his friendly advances.”