My roommate has recently purchased a pet turtle…any suggestions on how to tell whether it’s male or female?
What kind of turtle? In many turtles you can tell the male because the plastron (bottom shell) will be slightly concave towards the rear… also the male has a longer, thicker tail. In some Box turtles the males will have red eyes.
Ask it.
See if it leaves the toilet seat up.
It depends on the type of turtle of course. Look here to start.
Or, worse, leaves the seat down and pees all over it.
The male turtles are the ones that shave and the female turtles say “hey you cut yourself.”
Seriously I thought turtles were full of samonilla and that is why they aren’t sold as pets.
They are full of Salmonella. More than that, I cannot say.
Box turtles can be differentiated by the color of their eyes.
Have it watch television…
If it watches “The View”, it’s female.
If it watches “Three Stooges”, it’s male.
simple 'nuff!
The turtles that no longer can be sold as pets, since the 1970s, are the cute little baby ones, the ones the size of a quarter that used to be sold at dimestores all over the country for 50 cents. By federal law, pet turtles have to be at least 4" across the shell before they can be sold.
This is because in the big turtle-breeding and raising facilities, where they were raising thousands of baby turtles (mainly red-eared sliders, because they breed easily in captivity), there were of course problems with overcrowding and cleanliness, and in crowded, dirty conditions, salmonella breeds very nicely, thank you.
You’re still supposed to wash your hands with soap and water after handling your turtle, because they do still carry the salmonella bacteria in their feces, but there is no longer the problem with automatically getting sick when you bring home that cute lil baby turtle dripping with salmonella.
To address the OP: Epraz, ignoring all the facetious people in this thread, there really isn’t any good way to tell turtle gender, outside of a thorough internal veterinary examination, which I doubt your roommate is qualified to do. Just enjoy the turtle for what it is, regardless of its gender.
Here are some general guidelines, so you can entertain yourself making guesses, but there aren’t really any “rules”.
http://www.turtlecare.net/gender.htm
http://www.geocities.com/RainForest/Vines/5504/malefemale.html
If its a Chelys Galactica, then you’ll need to build a huge rocket, load it with a bad wizard and a Chinese tourist, and launch it over the edge of the world in an attempt to get a good look at the naughty bits. 
Since when do they call inhabitants of the Counterweight Continent “Chinese”?
Oh, um… how to sex a turtle. Right.
Show it gay porn. If it retracts its head into its shell… no, that won’t work.
Have it hang around outside in mid- to late spring. If it suddenly seems to want to go in a certain direction for no apparent reason at all and insists on doing so, it’s probably male. Mating season, doncha know.
Cut me some slack will ya? I thought my post was obscure enough for some people without throwing in the Counterweight Continent. Next thing you know, you’ll be jumping all over me for saying that this isn’t a good time for Johnny Klatch to be in flight school.
—ing perfectionist, Urinating Dog, Urinating Dog.
So ummm. . . What do the female turtles do while the males are off mating? 
Nuh nuh nuh, the chicks is where the dudes are headed. I’m trying to remember where the heck I read the anecdote about a guy having a wild turtle in his yard that had a high fence around it, but every spring the turtle would head over to a corner of the fence and try like hell to climb it, 24/7. Then a couple of weeks later he’d calm down and go back to his regularly scheduled turtle existence. I figured most turtles probably did the same thing.
[tangent]
pcubed, It sure as hell f*cking isn’t. What are you thinking, putting him into flight school at a time like this? Did you take stoopid pills this morning?!
[sub]Who’s Johnny Klatch?[/sub]
[/tangent]
[tangent continued]
No, but I did take my dried frog pills.
Okay, if you read further into the Discworld adventures, you get several real world analogies. Like the Counterweight Continent bearing a remarkable likeness to China in Interesting Times (complete with dragons, invention of fireworks, a written language made up of pictograms [like Urinating Dog for an exclamation point], etc.) and several references, most notably in Jingo to Klatch being an analogy to Arab states (hence the transformation of the British “Johnny Turk” into “Johnny Klatch”).
Now, I hope you didn’t take my “—ing perfectionist” to be any sort of personal attack, which judging from your reply you might have. 'Cause buried in there is yet another Disc reference (along with the aforementioned Urinating Dog). In The Truth, the character Mr. Tulip (of Mr. Pin and Mr. Tulip fame, who bear an uncanny resemblance to Mr. Croup and Mr. Vandemar from Neil Gaiman’s Neverwhere) is constantly going off about “—ing zombies”, or “—ing dwarves”, or “—ing poor representation of early Century of the Fruitbat shading techniques”. Written exactly like “—ing” and apparently sounding like that too. You get the idea. No offense intended.
I knew I would get into trouble if I went too deep into Pratchettland for a reference.
[enough with this tangent already, there are poor turtles out there wondering who to mate with]
I’m not sure if this is true for turtles as well, but a way to tell the sex of a frog is to look at the circle close to the eyeball of the turtle (sort of like a temple). If it is larger than the eyeball then it is male.
[sub]Wait until the turtle is having sex. The one on top is…[/sub]
This thread is about goddam turtles, people. And it’s about sex. What the hell are you talking about?
(That was a rhetorical question. If you answer it in this thread I’ll have you banned. JillGat - GQ moderator)