Just because we can do it, however, doesn't mean that we should--and here you'll find a list of ten Stupid Flash Tricks that you can create in Flash, but that you may want to avoid unless you enjoy driving your viewers away.
1. Blinking Text
The first time you learn how to make text blink, you may point and giggle and think "That's cool, look what I did!" By the tenth time that your viewers have seen blinking text overused in one website or another, however, their first instinct will be to close the site without even reading the obnoxiously flashing, eye-searing text. You may think that making your text blink draws focus to your content--but all that it draws focus to is how annoying blinking text is. Avoid this unless you want your website or animation to look like it was culled from Crazy Al's Overstock Mattress Warehouse.
2. Rainbow Gradients
To this day I wonder why Macromedia even bothered including a preset rainbow gradient, especially such a bright one. If you're really determined to use every shade in the ROYGBIV spectrum, find a way to incorporate them tastefully; don't just slap a rainbow gradient on something and think it looks cool. There are places for rainbows, sure--like in an actual rainbow. But if you're just using one because you can it and it has no real use in your scene or in your design elements, try something a bit more subtle, and a bit less blinding.
3. Cycling Background Colors
In my opinion, there is no better way to ensure that 90% of viewers will close your site/Flash movie within the first five seconds. Pick a background color. Stick with it. Cycling through background colors, whether they shift sharply or fade from one to the other, is a good way to either a.) give your readers a seizure, or b.) make it impossible for them to focus on the text or objects laid over that background.
4. Constantly Looping Sound That Can't be Turned Off
Embedded sound in Flash is basically the mutated, inflated younger sibling of the age-old and hated embedded MIDI background music. Flash has sound for a reason--for sound effects, for playable music files, for any number of myriad uses...but I'd bet money that Macromedia never intended for it to be used to drive people crazy with repetitive, looping, loud, irritating audio that can't be shut off without either turning off the volume on your computer or else just closing the page entirely. If you want to add background music to your movie, especially if it's fitting, go ahead. But make sure it's either quiet and unobtrusive, or else that you include a control to turn it off. There are few things more painful than loading a page only to suddenly be drive-by soundblasted by screaming audio at maximum volume.
5. Obnoxiously Persistent Animations
This is another "next-generation" version of an old annoying-but-persistent website no-no: the dancing, non-stop, ever-present GIF animations, now all grown-up and ten times as tenacious when implemented through Flash. Your web page or animation does not need constantly dancing doo-dads, especially if you've got actual relevant content that you want people to read. It's cute? That's nice. It'd be a lot cuter if you set it to stop after one or two cycles instead of leaving it to loop constantly as a distracting and irritating little aside that isn't at all necessary.