damn with faint praise
Compliment so feebly that it amounts to no compliment at all, or even implies condemnation. For example, The reviewer damned the singer with faint praise, admiring her dress but not mentioning her voice. This idea was already expressed in Roman times by Favorinus (c. a.d. 110) but the actual expression comes from Alexander Pope's Epistle to Doctor Arbuthnot (1733): "Damn with faint praise, assent with civil leer, and, without sneering, teach the rest to sneer."