I think you need to provide the context for anybody to answer that question. But it could mean: 1. a big explosion 2. someone or some people getting into a big argument 3. someone or some people getting angry. The use of "mega" is to exaggerate the size and magnitude. So, I'm guessing that you got this from a kid's book or an advertisement.

hi how are you ? i'm imed doctor from algeria i'm 29. i can help you with french,in the same time i wanna be a friend with you and learn english with you, if you wanna contact me this is my skype: imed_dr1

Maybe like a big explosion ?