The guy who:
* buys a crazy-cheap roundtrip ticket on Spirit;
* plans on stowing a carry-on bag in an overhead bin;
* can't be bothered to pay $35 in online-checkin for the bag; and
* can't be bothered to pay $50 at the ticket counter for the bag.
Because that guy will get to pay Spirit $100 at the gate. Each way.
Don't be that guy.
* buys a crazy-cheap roundtrip ticket on Spirit;
* plans on stowing a carry-on bag in an overhead bin;
* can't be bothered to pay $35 in online-checkin for the bag; and
* can't be bothered to pay $50 at the ticket counter for the bag.
Because that guy will get to pay Spirit $100 at the gate. Each way.
Don't be that guy.