Here’s the history: In the 1970s, the U.S. Supreme Court under the Chief Justiceship of Warren Burger started to develop the doctrine of “animus” as a way to find certain state and national laws unconstitutional. This was a kind of compromise position, by which the Court majority refused to extend the traditional kind of protection provided by the Fourteenth Amendment — by simply widening the number of groups whose treatment was subject to the most exacting kind of “equal protection” analysis, for example, because their situation was comparable to the situation of the formerly enslaved people who were the most obvious subjects of the equal protection clause in the Amendment, or, as in the sexual-liberty cases Griswold v. Connecticut (birth control) or Roe v. Wade (abortion), by widening the scope of the “due process” clause of the Fourteenth Amendment to cover a greater range of human activity.
The first big case had to do with “hippies,” and a national statute Congress passed in a Nixonian fit of pique against unrelated people in a household together who might receive Food Stamps to defray their grocery costs. (For a discussion of the whole string of cases, see this review) The case was U.S. Department of Agriculture v. Moreno (1972), and the Court ruled that the costs of the distinction between all-related households and households with some unrelated people in them could not be imposed on the population on the basis of distaste, or hatred, for a particular group — actually, a subgroup of the unrelated people who would lose benefits as a result of the law, since, as it was demonstrated in the case, there were plenty of non-hippies who domiciled together for various reasons.
The next really big case on this, which is still referenced by the Court today, has to do with disability. The case is City of Cleburne v. Cleburne Living Center (1985). The Supreme Court held in that case that a city in Texas couldn’t create a distinctive zoning process for institutions for people with cognitive disabilities (like the group home, the Cleburne Living Center). But rather than say, what was at issue in the city’s distinctive standards here was a “suspect” or “quasi-suspect classification” that ran afoul of the Constitution (as a classification on the basis of race or religion would be “suspect”), the Court majority said that there was “animus” afoot. And that animus, that ill feeling, bias, stigma, social rejection, could not be the basis for constitutionally legitimate government action.