Here is a GREAT TIP on picking out an eggplant!
I learned this on a food tour in Seattle and I really want to share! There are probably people who already know this, but I am sure there must be some who don't :-) (I sure didn't know!) :
Choose a male eggplant. Males have less seeds, so they will be less bitter.
How to know if your eggplant is male or female? Look at the bottom. If there is a brown circle it is a male. If there is a long brown mark (like a slash) then it is female.
Pretty neat, huh ;-)
I hate to deflate your euphoria but there is no such thing as a male or female eggplant. That would be like saying there is a male or female egg or uterus. All eggplants are fruit and contain the seeds of the plant. They cannot BE a sex, but they have developed through a sexual process - male flower parts fertilized female flower parts and voila! Eggplant. But the eggplant itself is NOT any sex whatsoever. Sorry.
On the other hand, there are differences in eggplants that may or may not have to do with the way the bottom looks. Some have more seeds than others - and the less seeds the better flavour and texture. So if the trick you mention works to figure out which are the seedier eggplants, great. But it ain't sex we're talking about here.