Wtf is 'mean six' meant to mean?

You're now chatting with a random stranger. Say hi!
You: do you like cheeesssseeee????????
Stranger: hi
You: cccheeeesssseeee??????
Stranger: yes
Stranger: u r boy or girl
You: thats so coooooooooooooool
You: i both
You: chehehehehehehe
You: ^_^
Stranger: mean six
Your conversational partner has disconnected.