1. unmoved or unconcerned; not caring; uninterested
1. He was indifferent to the concerns of normal people, and cared about nothing but making just enough money to survive in his small flat full of books.
2. mediocre; poor; not very good
2. He was a brilliant novelist, but an indifferent poet.
in (not, opposite of)#differre (to be different) (Latin)
A girl always looks for a guy who is different from the others, thus if he is in (not) different, he is MEDIOCRE hence she will be UNMOVED AND UNCONCERNED BY his proposals. :P