Stop El Capitan from asking to report to Apple every time I force quit an application
Using defaults write com.apple.CrashReporter DialogType none really should disable it, just like using defaults write com.apple.CrashReporter DialogType crashreport should switch it back on.

However, if it's not working for you, you can try the following two commands:

launchctl unload -w /System/Library/LaunchAgents/com.apple.ReportCrash.plist
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.ReportCrash.Root.plist


To undo the above change, you would use the same two commands, but replace unload with load in each.

Use a notification instead

Removing the Crash Reporter may be overkill for some users, so another option is to change this to a notification instead. To do this, use:

defaults write com.apple.CrashReporter DialogType UseUNC 1 

The advantage of this is you still get notified if an app has crashed, but you don't have to respond in any way (nothing to click on). To undo this change you would use the same entry but replace the 1 with a 0.