It really depends.
This is what I think makes a "bad" bump, as far as what I have seen so far, as far as reactions.
*Stupid bump reasons (ex. LOL
)
*Completely unreasonable bumps of ancient topics (over a year old.)
*Bumps of topics containing flame wars or bumping one to put in your two cents.
*Posting in an addon, that can barely be called one, asking for a link, of which the addon was a good 6 or more months old.
I know there are plenty more, I just can't be bothered to post the rest.