The reply you make to 'How's it going?' when you have no interest in having a conversation, or are having a day so shitty you can't even bring yourself to lie and say 'It's going good'.
Customer: "How's it going?"
Cashier: "It's going."
The most common excuse men use when their girlfriends/spouses discover their porn.
GF: I found a porn app on your phone, wtf!
BF: My friends put it there as a joke, I swear! I don't know how to delete it!