1) Install google chrome
2) Install the Linkclump extension for google chrome from the chrome web store
3) Install Tampermonkey
4) Visit this url and install the module using tampermonkey.
5) Edit sagi.execute("customurl"); to be sagi.execute("ggssx");
6) Enable the tampermonkey module you just edited.
6) Open a steam group that you want to send mass invitations to ggs.sx and make sure you login.
7) Hold right click and drag the linkclump box over the steam users you wish to mass invite
8) Open all the page urls and wait for them to finish loading then close
9) You have successfully been a prick and invited everyone to the ggs.sx steam group. Keep in mind this will only work once every 24 hours per 200 invites.