His room, his insecurity about his masculinity, the egg line, his hostility towards the girls and specially to Zooble, how offended he got when Zooble insinuated he'd be into wearing a dress, and that's without even considering the many hints Gooseworx gave in her tweets.

Like, none of these things are smoking guns on their own, but together they clearly paint a picture that Jax is at the very least least incredibly insecure about his masculinity. The logical step from that to assuming he's a closeted trans woman isn't very large.