A friend and I were indoors at a place…it was dark, but “black lit.” He said the glowing spots on my t-shirt were semen stains. I say no way, I washed it.
What say you?
So…you haven’t found the answer to this experimentally yet?
Pullet
A girl
Aaargh…took too long to edit…
It should read like this:
A friend and I were indoors at a place…it was dark, but “black lit.” He said the glowing spots on my t-shirt were semen stains. I say no way; I washed it.
And that’s the main question…does semen wash out of t-shirts after one typical wash in a washing machine?
What other (common) things might have caused the “blacklighted” stains?
Inquiring minds 
I would but 1978 called and asked for my black light back
Seriously, though, if I had one I’d perform the test…all in the name of science
You can get a new blacklight for like $12 at Walmart.
It’s all in the name of science! Do it!
I’d like to reiterate something I’ve mentioned over and over. People always think all the stains on the comforter/tshirts/walls etc etc that glow under a black light are seman. Well, laundry detergent glows also. The stains on your tshirt or probably just left over laundry detergent.
Almost any organic material will glow, to some extent, under a black light. The stains on your shirt could equally well have been drool, or food, or blood, or possibly sweat (I’m not sure about that one). You know better than we would how recently you would have been in contact with any of those substances.
I heard club soda glows, too. Did you have something with club soda that you spilled on yourself? Was this a club that stamps your hand so you can get back in if you leave? Because they usually use a fluorescent ink and if you rubbed it on your shirt then it would glow. Highlighter ink also glows.
I second the laundry detergent Idea.
Too lazy to find a cite right now, but I believe Modern Laundry detergent contains phosphorous to ‘make your whites whiter and your colors brighter’. It shows up under a black light as glowing specks on your shirt.
Also, jip stains are nearly impossible to get rid of. 
A little off topic but I encountered a bathroom in a Dublin pub that was heavily black-lit, and urine certainly flouresces.
[Mitch Hedberg]
I was under the impression that that mustard stain came out.
[/MH]
Many detergents contain additives that are UV active. They enhance the whiteness of your whites.
Without having actual experimental evidence, I’d wager that most ahem protein based stains should come out under normal washing conditions.
Do you have any reason to believe that they ARE semen stains on your shirt?
I took the statement “No way, I washed it” as evidence to support a “yes” answer to that question.
Nevermind.
I don’t think it’s club soda, but tonic water that you’re thinking of. The quinine in tonic water glows under black light. Club soda’s just water and CO[sub]2[/sub], sometimes with salt or baking soda.
[Once More, With Feeling]
♫They got
the mustard
OOOOOUUUUUUT!♫
♫(They got the mu-stard out!) ♫
[/Once More, With Feeling]
My vote is also for detergent. Sounds like you’re packing your washing machine too full for a good rinse cycle, and it’s leaving stuff behind.
Maybe the cat is humping your laundry.
There was a nice Youtube video along these lines.
A young lady was at a party, dancing as you please… one of her girlfriends pulled her aside and she left.
The young lady had a bright spot spreading beneath her skirt… and glowing on the left side of her mouth…