To me, "funny" becomes "offensive" when the joke is "ZOMG, that woman's a DUDE, dude!" rather than actually joke with any originality. Go ahead, make jokes
about trans people. Just don't make the joke
be the trans person.
Also -- wow, what crappy execution -- hmm, you're going on your honeymoon, and you're
just now finding out that your wife uses a Freshette?