Can wry humour be classified as "sardonic"?
Wry humour, sardonic humour, and tongue-in-cheek humour can be considered similar forms of humour. As windsor has said, sardonic humour is more sarcastic, more intended to aggrieve. Wry humour has a touch of irony, and there is little or no negative connotation unlike sardonic humour which in practice often has a negative connotation.
Tongue-in-cheek humour is very broad, and straddles the abovementioned categories. It implies something that is not to be taken at face value, whose meaning lies between the lines, and the humour is perceived when one uncovers the underlying meaning behind what is said. Often involves word play, where the same word or phrase has two meanings.
Wry humour, sardonic humour, and tongue-in-cheek humour can share common elements of irony, sarcasm, or even some element of contempt to varying degree depending on the context. Coincidentally, these are forms of humour that SBF forummers often fail to understand or appreciate.