Materialize Michael Jackson on Lyoko. That gets rid of two problems: PO'ing XANA and getting rid of Michael Jackson.

Put XANA's name on an internet dating site. Advertise him as a "Sexy young lady with lots of money."

Go to internet forums and advertise a petition for "n00bsp3k lvrz." Have them send e-mails entirely in Noobspeak to XANA. Daily.

Start by taking a computer game and installing it into Xana himself. Then, make him the weakest but most respawning boss in the game. Then just start killing him randomly until he shoves you out of Lyoko so he can clean himself off from the game.

Or just bang him over the CPU with a crowbar for a while.

Make the song from the SpongeBob episode Sing A Song For Patrick
play on the speakers 24/7!

Recheminez the programs of Xana in Babel, change the language into French, translate it in English again, and observe it as any Xana indicates is hopelessly deformed. (Reroute Xana's programs into Babel, change the language to French, translate it back into English, and watch as everything Xana says is hopelessly garbled.)

Bring in a bunch of magnets and have fun.

Shove a game cartridge into the processor. When it doesn't work, complain to Xana that the supercomputer is 'obsolete.'