27a - I'm puzzled by this as well. The best I've come up with so far is that it's a 3 letter anagram/"preposterous" of a synonym for "trick" inside/"bores" a 3 letter word for "stupid".
dylan, 12D - oddball relates to an anagram, so the first 3 words indicate most of that, and the subsequent two words provide the final letter that is needed.