Presumably because the dad who is wearing the princess dress on 'Princess Day' to make his child happy, does not look entirely comfortable wearing said Princess outfit, therefore it is transphobic because he has not fully embraced the situation (and is now demanding that everyone accomodate his demands.)
Who the fuck knows. No doubt this post will be on twitter in two minutes as more evidence of the transphobia on mumsnet. I think Birdseye have blocked a few of them for trolling, which is rather amusing.
Would love to be in the next BirdsEye strategy meeting..... "And So, next on the agenda: Is it worth pissing off 12 Million mothers who feed their kids fish fingers and chicken dippers so that we can be seen as 'woke'. Anyone? "