Post 390’s service is polite and extremely attentive. The night the ribs arrive cold, we inform our waiter. Before we know it, a guy dressed like a Secret Service agent is at our table, a grave expression on his face, asking question after question about what went wrong. He comps the ribs. Occasionally, servers can be a bit clueless. One evening, each time we order an item, our waitress reiterates, for no apparent reason, “The portions here are really big.’’ By the fourth time, it’s hard not to laugh. Another night, when asked where Point Judith is, a waiter begins theorizing, talking over a customer who is saying “Rhode Island. Rhode Island. Rhode Island.’’