Is it illegal to bomb students with joking information?

You think a little too much. It is normal to make some jokes or say something in the group. There is nothing illegal. You are not a public figure, and you are not an influential person. Your words won't bring any bad influence. Don't think too much.

It's not illegal, as long as it's against illegal people, such as those who maliciously advertise and invade others' privacy, there's nothing wrong with it.

But if you use a bomber to blow up other people's text messages for no reason, then you are waiting to be investigated.