Well Since Mini has already scared Diana on this...
I have thought about being a pyromancer...burning stuff and other random crazy acts of violence...
The worse thought is this though...
I cannot stand my best friend's boyfriend...he's worthless, cheating on her, abusive and downright one of the worse people I have ever known. I got sat down and plan out the perfect murder. I sneak into his house, or find him in the street and knock him out and drag him into the trunk of my car. Hours pass by and he wakes up strapped to a chair in an old abandoned warehouse. Essentially what I would do is: use pliers to rip out his teeth and tongue, I'd use one of the cigar cutter to slice off each finger one at a time and then use a blow torch to sear off the wounds so he wouldn't bleed out, I would then do the same to his toes, after all that I just take a baseball bat and start break his bones all over the place. After I beat him half to death, I'd just leave him to starve for a few days...after which I would politely just end his life and then shut the warehouse and walk away. I might set his corpse on fight to...not to sure though.
Now why wouldn't I do this...*sigh* sadly I have no warehouse...and plus my friend would have to move since he's all she's got in terms of a place to stay.
And now ya'll know...hopefully I didn't scare ya'll :3