When I first heard this I thought "¿De que hablas willys?" That's the Spanish translation for "Whachu talkin' bout Willis?". I thought those of you who remember "Different Strokes" might get a kick out of that. Surprisingly, the show was titled Blanco y Negro in Spanish.
Anyway, I digress. Back to our tenis.
Tenis is the word you'll want to use for what we call, or at least used to call, sneakers. Any type of "tennis shoe" is called tenis. Be sure to use the Spanish pronunciation.
Chafa means that something is of low quality, poorly made (de muy mala calidad). I believe the word we would use is cheap.
Marca simply means brand, as in a brand name, like Nike. When you say something is "Marca patito" , that means it's not a name brand product. We might say it's a generic or off brand.
So now let's translate the entire phrase:
Mis tenis son chafas, son marca patito
My tennis shoes are cheap, they're an off-brand.
It should be pretty easy to incorporate these new words into your Spanish. You'll sound "muy Méxicano", because these two words are very Mexican, and I doubt you'll hear them from anyone who isn't Mexican or spent a lot of time around Mexicans.
That's it for now,