In lab, I was talking about Phylum Nematoda. I mentioned to my students that while some of them are free living, many nematodes are parasites. I also told them that if they wanted to see some really disturbing pictures they should do a Google image search for Ascaris.
One of my more impatient students whipped out his iphone and did so right away. Then he showed the pictures to his lab partners. As expected, they were grossed out. What I didn't expect was that the guy would save this picture (click if you're feeling really brave - if you're not, it's some roundworms coming out of a kid's butt) as his phone's wallpaper.
Him: That was so gross. I couldn't believe how many worms were coming out of that man's butt.
Me: You mean that little boy.
Me: That wasn't a full grown man.
Him: Are you sure? I thought it was a man.
Me: Dude. You of all people ought to be able to recognize a young boy's anus when you see one.
(I'll leave it up to you to decide if this is true or if it's an April Fool's joke.)