1756, hob and nob "to toast each other by turns, to buy alternate rounds of drinks," from c.1550 hab nab "to have or have not, hit or miss," probably ult. from O.E. habban, nabban "have, not have," with the negative particle ne- attached, as was customary. Modern sense of "socialize" is 1866.
[hob-nob] 
verb, -nobbed, -nob⋅bing, noun 