'), but the rule holds better than most English rules of grammar and structure. Your two adjectives don't modify each other; they both modify 'teacher'-- or at least I presume that is the intention, and should be separated by a comma: 'a funny, angry teacher'. If you want to modify an adjective (and words do not simultaneously describe each other) then you should use the adverb: 'a funnily angry teacher' (though I caution you that this particularly pairing is a little awkward sounding here, perhaps because it is difficult to see funniness in an angry teacher, especially when you are the student).
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