Advanced Gaming & Theory: Handedness?
Sometimes it can be helpful to a dungeon master for a character to have a favored hand written on his character sheet. This can quickly solve some arguments which might pop up over throwing stuff while still armed, as well as some odds and ends.
Now, we both know that if we just let characters specify what hand they favor, then they will always claim to be ambidextrous, which we just can’t have. That and I love charts that allow us to use our poor and often neglected 12-sider.Roll—Handedness
1-9—Right Handed
10-11—Left Handed
12—Ambidextrous
Personally, I like rules that are easy enough to remember that you don’t even need a chart, so in my work-in-progress system you roll 2d6. On doubles you’re left-handed, on a 12 you’re ambidextrous. That gives results that are quite reasonable, and I can remember it off the top of my head.
I use the same method for determining sexual orientation for NPCs (or PCs that want to roll). That probably overstates the prevalence, but re-using a rule is even easier than remembering a new one!
Tales of the Rambling Bumblers 
My opinion is that, unless there’s a built-in game option (such as the Ambidextrous Edge in Savage Worlds) the simplest way to go about it is to make the character have the same handedness as the player.
While that’s simple, that doesn’t serve for NPCs, nor for players that want to leave it to chance. Plus, it gives you a chance at an ambidextrous character, which is often an advantage even if the system doesn’t explicitly have rules for it.
I think you are drastically understating the numbers of both gay and bi folks. But it may be just that I live in Seattle and may be dealing with a self selection issue. I like the idea in general and will adopt it in my games. I will add the proviso that the results indicate the public orientation of the person in question.
For handedness in the absence of SW like edges and such this is perfect.
I think it probably is a selection issue; I don’t think I’ve ever seen even a gay advocacy group claim higher than 10%, and the rule I proposed actually works out to close to 14%. Certainly that’s good enough for gaming, though the GM naturally should modify it for different cultures and sub-cultures.