It's about being aware that one has such models. Everyone does - it's part of the way humans build models to abstract and generalize; this is why it's possible to get up, get breakfast, and head to work while thinking hard about a problem: we can default a lot of actions to automatic responses and get along pretty well. It's only if something isn't as we assume (shower breaks, no eggs in the fridge, someone slams on the brakes in front of you) that we get in trouble.

Assuming that someone likes flowers is really not that a big deal. But assuming that they're not good at math, or that they represent every person that fits into a given group, or that they're comfortable with the same behavior or language, or any number of other things is a very big one. Not taking into account that you have a model, and that if you don't think about it, it will get used, will result in it being used to make a lot of default assumptions, some benign, some not.

As the public representatives of Perlmonks, we need to try to present the best face we can - because people who see us are humans too, and just as likely to form opinions about groups as anyone else. If we thoughtlessly use language that says "I'm not thinking about this group as a whole lot of different individuals who happen to share a common, easily-identifiable characteristic, but as all the same", then people observing us start building mental models that say, "the Perlmonks folks don't care about/don't like people who are X" (female, who don't speak English well).

If on the other hand we try our best to not do so, we help people build models that say, "Perlmonks are pretty nice people who care about understanding individual people".

It's only if something isn't as we assume (shower breaks, no eggs in the fridge, someone slams on the brakes in front of you) that we get in trouble.

Not all, only the impaired and unprepared :)

When an assumption fails, the prepared STOP

Stop Think Observe Plan

I heard it from some old white woman, who heard it from some bearded white guy , on the internet

That is right, when I am asked who I heard it from, humans want to know that someones status ( man/woman/race/age/bona fides)

Being a human, living with humans, I look at and remember faces, and with faces the information man/woman, color/race, hair, clothes....

So when someone calling themselves girl asks about drawing flowers, naturally we remember some girl , not some body

So some girl, I assume doesn't mean anything other than, it must be some human girl, don't know what she looks like or anything else about her.

It doesn't mean anything negative

All that psycho-knee-jerk-huu-haa is knee-jerk thoughtlessness, by jerks who assume calling a girl a girl is calling her bad at math, and other stupid things

You heard it from a dog

Good points.

I would like to reiterate that Jung explains at great length, the Anima and Animus, and how it is part of our psychic development as living beings. When we sey "feminine", we mean Anima, and so too with masculine and Animus. Hence, the assumed masculinity and femininity are not like any other group assumption, they are part and parcel of the human race.

Hence, in this case, i see no problem with the assumption. Though i would likely be agitated about any other grouping.