My uncle asked for my social security number for his son's food stamp?
If you are in the same house, but are not sharing food, it should get marked as separate household, in which case, he does not need your number at all. If you are sharing utilities, they will need to give a name, but not the SSN. Its entirely possible that he is confused, because the paperwork usually says, Please list SSN for all people living in the household. The difference is, what is the definition of household? Sharing food & utilities counts as same household. If you are not sharing food, then you are separate households, and he does not need your SSN.