In short, killing a comment thread. This can occour many ways. A few examples are: going completely off-topic, posting a very long comment, or posting any comment that makes other commenters feel as if they just shouldn't add another comment. Comment bombs are often dropped by a thread killer.
Bob: "HAHA! Funny picture!"
Sarah: "Lol, I remember when this happened!! =)"
Jared: "I'm sorry, I just can't laugh at this right now. I'm so depressed."
Jared: "I feel so alone... Someone hold me"
Jared just went comment bombing.
To click the post comment button thousands of times to give someone thousands of comments on MySpace.
Suzan dumped me so I comment bombed her 3000 pictures of a fat guy in short shorts. Ha Ha Ha.