A witty remark is clever and funny and timed just right. When you make such a remark, you are also considered to be witty.
The adjective witty can be used to describe those quick little funny remarks that often demonstrate a sharp, biting humor delivered in a playful manner. Witty usually describes things that are off-the-cuff amusing, rather than remarks that are elaborate or carefully planned in advance. This adjective is usually used in a complimentary way, but, like its cousin clever, it can be used sarcastically, as when someone who doesn't appreciate your one-liners says, "Well, aren't we witty today."