why not " You are not horrible"?
Haha! My answer was: "Chan eil ugh grànnda" instead of "Chan eil thu grànnda" :) Thu and ugh sound so similar to me.
I must add that my answer was wrong, obviously - but it did give me a laugh when I saw the correct answer.
It feel it would be impolite to say this unless it was in response to a direct question like «A bheil am fèileadh seo a ’toirt orm a bhith a’ coimhead reamhar? »