Not that the tweet was the most egregious sample of transphobia ever, but seriously, transgender people asking for their gender identity to be respected is a really stupid damn thing to satirise. Satire is supposed to draw attention to real social problems so they can be improved, not be used as a thinly-veiled excuse to make fun of marginalised people.
It's also low-hanging fruit. He might as well have made a 'har har, I identify as an attack helicopter' joke.