BAWWWWW!

BAWWWWW! (number of "w" may vary, although it's generally set to five) is a furry onomatopoeia or text that appeared on a panel in Incontinent Student Bodies, a comic by furry artist Marci McAdam

Origin
As stated above, its origin is a panel from the comic ISB (issue number 2, first published in 2003), in which a juvenile rabbit in diapers has just wet himself begins crying inconsolably.

Usage
The word, as both text and as a image macro meme, is used as a response on a thread or discussion to imply that the person being mention or attacked (normally a furry fan or furry artist) is a "whiner." The term has being popularized by various individuals on various furry critical sites such as 4chan, Lulz.net, and Encyclopædia Dramatica.

Not solely a furry demeaning term, it's also applied to furry critics (trolls, griefers, mundanes), or nonfurs who take a contrary stance against such attacks on the targeted user in the thread (White knighting).