Java - Probably Java is the nastiest of all
Until few years ago you could not browse some web sites because some derailed 'web developers' decided to put some 'cool' animations and menus on their web site that required Java, forcing YOU to install Java, this way.
Now, Java is a really intrusive mammoth that starts at computer start up, installs background services, make your browser literary crawl eating A LOT of memory and keep wasting your Internet bandwidth by checking and downloading updates. And boy, Java needs updates because every 3-4 days a MAJOR security hole was discovered! And every security hole in Java is a security hole in YOUR computer.
ACTUALLY, Java is so dangerous for your computer that "The U.S. Department of Homeland Security is advising people to temporarily disable the Java software on their computers to avoid potential attacks" floridatoday.com
It is so bad that Firefox won't even let you activate it.
I uninstalled Java maaaaany years ago from my computer and I vehemently refuse to install it. Not a single time! And many others like me have forced the web designer community not to use Java on their web site. Now probably less than 1 in 5000 web sites still have Java. So, you miss it a bit.
Acrobat Reader - Big deal for nothing
Adobe Acrobat Reader is basically a notepad. Its task should be to open a PDF file and show it on screen. It does this in such a bombastic way that 3 minutes later after Acrobat, but it is still crunching data, you forgot why you wanted to open that PDF anyway.
Same bubonic 'features' as Java: eats up lots or memory and disk space, invades you with background services, system tray icons and installs itself to run at computer start up.
Security wholes? Plenty.
Alternatives: Foxit PDF (once a decent and fast PDF viewer, now starting to step on exactly the same sick path as Acrobat Reader), Sumatra PDF. More about these Acrobat Reader alternatives.
And something else: Next time somebody sends you a PDF send him an email back and say "I politely request to send me the document as DOC or RTF. They are as good as PDF" then optionally sign: "Fuck you and best regards retard".
Adobe Flash Player
The Flash Player literary built and shaped the web as we know it. And this is not the web should be.
Firefox will also deactivate the Flash plugin when a MAJOR security whole is discovered. And boy, coming from Adobe, there are lots of those!
Alternatives: HTML5 - After all those years, the web community is finally coming to its senses trying to replace Flash with HTML 5, a major update of (too) old HTML. This change should have been done 25 years ago (which on Internet time-scale means 2 eons ago).
Most web sites already abandoned Flash and switched to HTML 5. So, it is not the time to turn off the Flash plugin in your browser and finally take a fresh breath of Flash-free Internet.
Also see "Flash is dying a death by 1,000 cuts, and that's a good thing" by TheGuardia.