It's a guy thing.
The first time I heard the term "yarn bra"–I think it was over at Marilyn's blog, where just about anything can happen–I blushed to the roots of my hair. Marilyn's not one to mince words, but the apparent mention of her unmentionables in a public forum still raised my eyebrows.
Now, of course, I know what a yarn bra is (peek at one here!), but I'm neither the first nor the last man to require clarification.
When I taught Willibald to knit, he found the term mightily amusing and suggested that if knitting were a male-dominated field we would instead have "yarn jock straps."
And then, when they came up in the comments about my runaway yarn on the Megabus, a non-knitting friend of mine wrote and told me he had honestly thought a "yarn bra" must be a brassière with an extra space or attachment for holding knitting yarn.
Whereupon I doodled the following in my sketchbook.
Men. We're all alike.