him/her? not really, through I can't say I care much about the gender of Manning, it's really rather irrelevant, it have nothing to do with why she's in prison, and if I was trans, I wouldn't really use her as representant of transsexuality and become angry every time someone mispronounce her gender (in fact I would be happy, because I would hope they didn't connect transsexuality with a traitor).
What the [Inks] is wrong with you?
It' really isn't that big of a deal. Stop looking for reasons to be "offended". Not being massively outraged whenever someone makes the (very understandable, btw) mistake of referring to a pre-op transsexual who was well known as male as such isn't "transphobia". It's a very basic slip of the tongue.
Calling you anything other than a horrible person would be a very basic slip of the tongue, but I generally manage to avoid it.
