Differences between manga male and female characters?

One thing I can't find anywhere are what details make female and male faces different.

When we're talking about the whole body, the business is pretty simple - girls have specific silhouette shaped like a hourglass, wider at the waist, thinner at the belly and then expanding a bit again at the chest. Guys have even simpler body structure than that.

However, I can't figure out how to draw faces to make it easy to guess the gender at first glance. This is quite important, as I prepared a story which features few... um, gender-flipping arcs (because it's a goldmine of hilarious scenarios), and thus I need to draw in a way that will let anyone immediately know that something's not quite right with the character.

Any suggestions please?

This is how I would go about the whole construction of the head.

First you draw a circle for head construction reason like you normally start and with the line going down the center of the circle to show where the nose and bottom of the chin are going.

If you are drawing a man, have two straight lines drawn directly downward or at a very acute angle inward about 1/4-1/2 an inch. Continue a set of curves that would move ever so slightly inward. When you reach near the bottom of the line where the chin is supposed to be, draw a straight line to have the chin look like an edge of a block. You can add sharp looking cheek bones to add some more masculine quality. You should see a very square like cleft and chin with a slight curve of the cheek.

If you draw a woman, you can follow the line straight to the point for a skinny face or for a more round face, add in the cheek bones by drawing a little outward but not to curve the lines so sharply and start from there.

Another way to distinguish gender easily is how the face looks. Long eyelashes and bigger eyes (in anime) suggest feminine qualities and smaller eyes and less eyelashes suggest masculine qualities.

I hope that answers the question. You should also look at other artist's works as well and observe other techniques they may use.

Well sir, you've successfully managed to clear my doubts. I'll even write these notes down to keep while drawing. Thanks.