As requested by @subtleseeker in comment, I will share how I exclude directories when doing ncdu command.

Basically ncdu has the same command line options as the du command, so to exclude a directory simply use:

--exclude /dir/path
For example: ncdu -x / --exclude /home/tmp

To exclude multiple directories: ncdu -x / --exclude /home/tmp --exclude /var/log

etc.

Note that you should avoid a trailing slash (use /home/tmp NOT /home/tmp/) otherwise it will fail to actually exclude the directory.