Well, as a French speaker, I understood "gai" as "gay". After all the question is:
"What's up with you? You look so stuck up/uncomfortable, are you high or gay, you'll end up like your brother".
"Happy" jut doesn't work in that meaning. And "tipsy" isn't a common meaning at all. "Gay" is actually more common as a meaning than "happy" nowadays. Of course, that's coming from a Quebecer's perspective. French people can have other interpretations.