Hilchos Lashon Hara, chapter 1, section 8, 9

The prohibition of lashon hara applies whether a person actually says it out loud or writes it in a letter. It also makes no difference whether the lashon hara is said openly or only hinted at. All of these are lashon hara.

Also know: even if a person puts themselves down while putting someone else down, it is still lashon hara.