The strange, often concerning behaviour that many
people exhibit following a break up with their significant other, and/or in response to the
jealousy of seeing them with someone else, in an attempt to cover up how
broken they are deep down.
It usually consists of trying to act happy, and like everything is perfectly normal, psychologically blind to the fact that they are acting anything but normal.
Named for the behaviour Ross Geller exhibits in the "Friends" episode "The One Where Ross is Fine"
"Man, Matt just broke up with
Stephanie yesterday and this morning he invited me to a concert next week and started talking about his plans to become a
YouTuber! Is he ok?"
"He will be, man. He's just got Ross-is-fine syndrome. Give him some
time to grieve"