Rice and beans, in case you didn't know, are very popular side dishes in Central America and a good chunk of the Caribbean. It also gave rise to the popular slang term to describe Hispanics: "beaners" (which ranks just a little below "spics" in terms of offensiveness). To put it in another way, to say "The next time someone offers you rice and beans..." to a Hispanic is akin to saying "The next time someone offers you fried chicken..." to a black person. Or watermelon, or whatever other food is used in other racist jokes. It's a crude stereotype (and as all stereotypes, it's based partly on truth and exaggerated to extreme levels) that in this context doesn't seem to have any sense of playfulness, just a venomous anger.