I'm not sure if I understood the context correctly, I think this works in Arabic:
أعلى ما في خيلك أركبه = [try to] ride the the highest (tallest/biggest) of your horses; used to say something like "I don't care and I'm not afraid of you, do something about it if you can". Just a guess, this might have originated in battle or horse races.
Less common is (روح) بلط البحر = (go) pave the ocian [if you can]. But this is used mostly when you know that your opponent can't do anything; it's like saying "tough luck, live with it".
Youths (mostly male teenagers) might say: لو رجال/راجل/زلمة تعال = if you are a man come. this phrase usually ends up with a fist fight.
In Dutch it could be something as "Laat maar komen". Backtranslated to English this gives (more or less literally) "let/have it come". I think that the Dutch phrase can also used in the context you gave, namely, in the context of challenging a rival or an opponent.