Can't double click from touchpad in Debian/Kali

Touchpad clicks are disabled by default on Deb systems and hence in Kali too. You can use GUI to goto

Apps-->Sys Tools-->Preferences-->Sys Settings-->Mouse and Touchpad

Enable Touchpad clicks from there, otherwise follow this link.

Update: In Kali Linux 2, you can go to:

Left Dock --> More Applications --> Settings --> Mouse and Touchpad