1. "Awesome" Fan Flash: I do not want to see anyone but Egoraptor making these. While many of the ones he made are funny (except for the Awesome Center and Crossing remakes); the fan made ones are boring, cheap, and unfunny (e.g. Awesome's Creed, Irod Bad, and both of the Brawl Taunts shorts). I don't mind video game parodies, but only when they're inventive or well-thought out.
Worst Offenders: the aforementioned Awesome's Creed, Irod Bad, and both of the Brawl Taunts shorts.

2. Sketch comedy collabs: It's true that these have great animation, but that cannot compensate for crappy jokes. This only worked for Blamformers, The Metal Gear Funnies, Skittles & shits, and Skittles & Dicks.
Worst Offenders: Nin10Doh! and The MGS Flash Collab.

3. Flash that relies on internet fads: Ugh, I don't like it when people use fad jokes as flash material. Those who use "Shoop-da-whoop", The "O Face" Smiley, or anything they got from 4Chan (which I avoid like Chlamydia), YTMND, YouTube, or whatnot have creativity as bad as the latest MadTV/SNL episodes and should be treated as such.
Worst Offenders: Super Mario Hyadain & anything Kirbopher did after Mario RPG: Rawest Forest.

4. Parody Videos: While I did like Konquest of the Kamidogu and Knox's Mortal Kombat; I steer clear of these simply because they aren't very funny. Plus, ]{ombat, Knox, and Bezo knew when to quit.
Worst Offenders: Transformers Bastardized & Naruto Super Dub

5. Excessive use of Filters: As I said in a previous rant called Thoughts on my Mind, I don't like it when a Flash cartoon has so much effects to the point where you need a PC that has the power of Six X-Box 360s in order to watch it in high quality. I understand that you want to wow the audience, but sometimes dumping assloads of effects is not necissary. Besides, nobody cares about special effects when your content is dog shit.
Worst Offenders: SMBZ Episodes 5 and 6.

6. Flash that has voices done by members of the Voice Acting Club/Alliance: While the likes of Egoraptor, Kirbopher15, Baron Von Brunk, The Reel Splatter crew, Cailen Denton, RTil (even though his profession is animation/art), the Zirbes bros., Chris Zito, and the NG Staff are worthy of the professional title; the vast majority of the voice actors on those forums aren't good when compared to the aforementioned guys, or the likes of Ian Corlett, Bernard Eckhardt, Scatman Crothers, Buster Jones, Susan Blu, and Jessica Calvello for that matter. I think Rtil was right when he said "Good Mic =/= Good voice actor."
Worst Offenders: Both of the Brawl Taunts shorts.