Can I eat ribs with a fixed retainer on the bottom?!

Yes, you should have no problems.

I have a fixed retainer on the bottom as well ^_^

are you talking about the inch or so long bar that they cement in behind your teeth? if so then yes. i had that when i got my braces removed and the only foods i really had problems with was breads and popcorn. meats sometimes got stuck in there but were easily removable. popcorn was a pain in the ***

if you're worried, just use a fork. if the ribs are tender enough it shouldn't be a problem. and if they're not tender enough, they're not worth eating anyway! : )