Need a good 'comeback' for..."How do you get that thing..."

[Joel Larsson]

Oh, but I've heard "Mooommy! Look at that big guitar!" quite a few times. I'd say I get a guitar remark for every two cellos.
I remember once, some kid gave me that guitar remark. His mother told him, "It's not a guitar, it's a cello!" She looked at me, a bit embarrassed. "Please excuse him. He doesn't know better."
"IN YOUR FACE!", I thought, but didn't say it out loud.