One Tomato, Please

One tomato, that's all I needed. I walked up to the fruit & veg guy and said

"Una tomate, por favor"

The other nearby fruit & veg guys started laughing. Were they laughing at me? Did I say it wrong? I met up with my Spanish friend, Celia, and told her the short (and somewhat dull) story. She started laughing, nearly busting a gut.

Greg - What is so funny?! Una tomate, por favor; one tomato, please... what's the problem?
Celia - Tomato is masculine. You should have said "Un" instead of "Una"
Greg - That's funny?!
Celia - Si.

Wow, that was a LAME story but at least you know how to ask for a single tomato, now.

P.S. I won a box of chocolates last night. BOOM.