Titanical

When something looks like a good idea but it's actually a terrible idea.

Person 1: Hey, you know what would be a halarious prank?

Person 2: What?

Person 1:Replacing all the water in those childrens' water pistols with sulphuric acid.

Person 2:Aw yeah do it!

*after, in jail*

Person 2: Well, that idea was Titanical.