While I understand you're joking...
I don't know how one would be able to prove Terrorism in a court of law...Inducing mass fear isn't a crime... Potential Genocide isn't a crime and if it was you couldn't prove it for Joker.
While WE know Joker did a lot authorities in gotham couldn't possibly know that he killed The Chechen or Lau; remember it was set on fire ad the DNA from the cigar that was used to light it would be the Chechen's plus Joker's goons put the Gasoline on.
Terrorism would be an easy charge to prove up. He carried out a threat to blow up a Gotham hospital. He took two people hostage (easy to prove, he gave their location to the cops), and blew up the buildings they were in, killing one of the two. He took two ferries hostage by threat of explosion -- which is terrorism regardless of whether they actually blew up.
The way I figure ... he's up for --
(1) Several dozen counts of murder (bank manager, fellow armed robber at bank, pencil trick, Judge, hockey-gear batman, Commissioner, Rachael, cops at jailhouse, guy in jail). Almost all provable -- video surveillance, video threats, personalized threats, revealing locations of hostages, "I want my phone call", etc;
(2) Several additional counts of attempted murder ... Mayor, Jim Gordon, Harvey Dent, Rachael Dawes (flinging her out a window);
(3) Terrorism ... hospitals, ferries/hostages, jailhouse, Rachael/Harvey (also almost all provable -- most threats were made by video or telephone);
(4) Terroristic threats (this is where the inciting fear thing comes in ... also includes hospitals, ferries, Wayne Enterprises lawyer, etc.);
(5) Murder for hire ... "kill the batman".
(6) Racketeering/RICO ... taking money from gangsters in murder-for-hire scheme likely qualifies under the Racketeering Influence and Corrupt Organizations Act;
(7) Armed robbery (bank);
(8) Extortion (Batman reveal yourself, or I kill someone);
(9) Breaking and Entering (Wayne Penthouse);
(10) Assault and Battery (Rachael, couple of old guys at Wayne Party, Harvey Dent);
(11) Attempted assassination (Dent, Mayor);
(12) Attempting to break someone out of police custody (Dent in Police Motorcade);
(13) Illegal weapons ownership (Bazooka);
(14) Incitement to riot (kill the Wayne attorney guy);
(15) Impersonating an Officer;
(16) Bribery of a government official (to get Rachael);
(17) Vehicular homicide;
(18) Reckless driving ...
Shall I continue? There is more. Kidnapping, hostage-taking, arson, etc. He's dead-to-rights on almost all this stuff. Most of it includes video threats, video surveillance, admitting to stuff in front of Batman/Dent/Gordon, and dozens of witnesses were left alive. He didn't hide any evidence, and didn't really try to. He'd get the better part of a millennium in prison, or a lovely padded cell at Guantanamo Bay, Cuba.
KBZ