To pollute the stream of a Twitter hashtag by tweeting a meaningless, satirical, or spamlike tweet containing the hashtag. Usage is comparable to googlebomb.
McDonald's marketers were horrified as #mcdstories, meant to solicit positive tweets about experiences at the restaurant chain, was twitterbombed with replies like "I ate a Big Mac and got the shits for 24hrs. #mcdstories"
When people following you on twitter get mobile device updates from your tweets. Most humorous when they are all in the same room.
During our meeting, I tweeted how bored I was and unknowingly sent a twitterbomb to everyone in the room.