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onion rings are a bit*$% to eat. You bite into it and the whole onion comes out and you are left with batter. yuck.

i actually dont eat either fries or onion rings though so to me I see no difference in a person who changes their order, I just lump them into "unhealthy".
 
substitute [their] fries for onion rings
If you leave out the word "their", and with no other context, I'd interpret this as "substitute fries in place of onion rings". In other words, I'd end up with fries instead of onion rings.
 
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