Yeah, I know that is probably the weirdest question you've ever heard... Why have an anti-virus installed if you want to exit it, right?
For some reason, just now when I was updating X-Split Gamecaster... Gamecaster refused to properly update unless 5 programs were closed. Among these were Dropbox.exe and Avastui.exe. I told Gamecaster it could terminate the programs, which it had no problem with other than avastui.exe.
I suspect it wanted to update some common component all 5 programs were using, so I looked for a way to manually close avastui.exe... including trying to terminate it through taskmanager. No go. I ended up having to uninstall it.
I am now in the process of reinstalling avast... -.-.
For future reference, is there a way to close avastui.exe temporarily?