Stashed in: Evil, gifs, Reaction GIFs!, Dr. Evil, Mike Myers, MFW, King of the Hill, Laugh!
That Jafar GIF is pretty sweet, but we can do better:
Hank from King of the Hill
Does this count as maniacal?
How about this one?
Oh! Found one! Army of Darkness!
Bonus points! Dr. Evil!
Dr. Evil's maniacal laugh dates back to his youth.
Al Bundy is laughing, but is it maniacal?
Bike Flip gif - At least he's wearing a helmet.
Dancing Dodger Fan
I hope all the bad things in life happen to you and nobody else but you. ~Dave Chappelle
Kittens climbing leg gif -- little derp in the background and the leg bite makes my heart melt...