First things first, THIS IS A 100% TROLL ONLY TO USE FOR MESSING AROUND! This is a build I made up really quick and told my friend to use, he had some good success with it I decide, "Hey, I might as well upload this **** to mobafire and see if anyone else has success with it!". So here is the trollish AP Twitch build that was made up pretty fast. Hope you guys try this out and enjoy it! Remember, don't expect any miracles because I sure as hell are not. Keep in mind when rating this build that it is placed in the humor section for a reason!

Pretty basic, Marks of Insight for that magic pen, because that stuff is pretty darn important! Seals of Alacrity for the attack speed, you'll get those stacks for expunge in no time. Glyphs of Celerity for cooldown reduction, so you can pop that expunge more often. And finally, a Quintessence of Insight for a little more magic penetration and 2 Quintessences of Force for a little more ability power.

The Masteries are pretty straight forward as well, mostly right down the ability power tree for offensive masteries and some armor and resistances in the defensive masteries. If you REALLY wanted to, you could of course go down the utility mastery tree a little bit and pick up mana per level and move speed, but I prefer the defensive mastery tree.

The Items. Now this is where I thought for a few minutes about this build. What items would be most effective on an ability power twitch? Malady and Nashor's tooth. Now these are the two KEY items in the build, ability power and attack speed. These two items are vital to this build and should never be swapped out for any other item.

Okay, now I like to start with boots and three health pots, mainly because I see no reason to start with anything else. Dorans Blade won't help you very much and Dorans Ring isn't that important either. Start working on your Malady, but get Zerker Grieves as soon as you can.

Once you have your Malady, start building up to your Nashor's tooth, these two items are great together and are seen a lot in Teemo builds.

Next I put a Rabadon's Death Cap, but if you find that extra health more important, grab the Rylai's first. You all know why this Rabadon's is here, more ap!

Now, get a Rylai's (if you got the Rylai's first, get the Death Cap now) this is, of course, for more AP and more Health, as Twitch is one of the squishiest champions in the game.

Finally, a Wit's End. This item is great due to it's passive and is paired very well with the Malady and Nashor's Tooth. This item is also very vital to the build and should not be replaced or modified.

If the game is still going on and your enemies are tower hugging for all that is holy, get some elixirs! Elixir of Agility for more attack speed and Elixir of Intelligence for more AP(and CDR)!

That about wraps it up for the items.

Skill Sequence, this is the only part of the build that left me derpin' for a little.

Of course you want to level up your Expunge first, get that to Level 5 ASAP!
Get your ultimate whenever possible.
After your Expunge is level 5, focus on leveling up your Ambush. That bonus attack speed is so... just so good.
Finally, get your Debilitating Poison to level 5, this slows your enemies and such, insuring they don't run away from you.

I use these summoner spells on practically anyone. Though if you feel it necessary to use Heal for Twitch's squishyness go right ahead and use it! You can also substitute flash for ghost if you want. Doesn't really matter, it's mostly personal preference for summoner spells anywho.

Pros
Very very strong
Great assassin
That expunge will be doing a lot of damage with 6 deadly venom stacks
Great roaming
Decent Early Game, Awesome Mid Game, Even Better Late Game (If not focused)

CONS
Super Squishy
May be inferior to standard AD twitch builds
Can't be focused
Not meant for serious play
It will make your enemies cry, and your teammates too for all the "kill securing" you'll be doing.

That about sums it up. This build was made up fairly quickly (in a matter of an hour) and is NOT meant to be taken seriously, although given the right teammates/enemies you will wreck with this build. Good luck, and remember to rate and leave a comment whether or not this build was successful! If this build draws attention to itself (which is partly why I made it, to see how many people I could get to troll around with AP Twitch) I might consider to make more troll builds with more thought and effort put in them. That's it for this build. good luck and half fun