My Frontier story:
Booked a plane flight last minute for a funeral. Never flown Frontier. Show up to the airport 65 minutes before flight. Approach counter. Two agents gossiping and laughing. Ignore me for a full two minutes.
Finally get to tell agents which flight I am taking and would like to check in.
"You have to check in using the app."
"Really?"
"Yep... only way."
Fine. Back off and start installing the app and using it to check in. Takes a few minutes. I'm not kidding - 59 minutes to flight, I hit return. App says I needed to check in an hour before and won't check me in.
Approach desk. They say, "Yeah, it's (now) less than an hour to your flight. We could have checked you in for a fee, but now we can't."
"Why didn't you tell me that? I would have paid the fee! I have a funeral to get to!"
"Sir... sir... you didn't ask. Now please leave the counter or we'll call over the police."
Never again. Screw Frontier.