Heh, I just found out than if you insert an empty pair of BBCode tags like [b][/b], you may disable smiley feature of the forum :)

Just put caret in the middle of those characters that just don't want to become normal text (don't select them), and press "B" (Bold) tool button (or manually insert the pair of BBCodes). This also works inside BBCodes themselves.

Hope it helps someone.

There is also an official way:

Oh! I'd better new it earlier!