If I Send My Friend In Mexico A T-shirt From The Us, Will He Have To Pay Anything To Receive The Gift?

I live in California. My friend is temporarily living in Mexico City, Mexico. I want to send him a shirt from www.threadless.com as an early Christmas gift. At the end of the page where you fill out the shipping information to send the shirt, it says, “Custom fees and additional fees may apply for international shipments. Please contact your local customs office for more information.”
I read somewhere online that they might charge, like 38% of the total cost to cover the customs officer’s work? That would be like $10! Does that mean my friend would be charged that or me? Is that even accurate information? Would I be better off having the package sent to me and then going to the post office and sending it myself, or sending it with his family when they go to visit him the week before Christmas? I just really don’t want him to be charged just to receive his Christmas gift because that would be really crummy!
I’m not really sure what/where my local customs office is, and if I can get an answer from you lovely people here, I’d rather not have to suffer through some phone research to figure this out.. Does anyone have any experience with this?
Thanks so much in advance!! =]
P.S. Sorry for the awkward categorization.. I chose Yahoo’s top suggestion because there doesn’t seem to be an area for Shipping & Mail-related questions.