American, very informal!

if you go ass over teacup, you turn upside down with your feet above your head.

She slipped and fell ass over teakettle down the hill.

• fall on hard times
• fall on stony ground
• fall out with
• fall out with someone
• fall over
• fall over yourself to do something
• fall prey to
• fall prey to someone
• fall prey to something
• fall short
• fall short of
• fall short of something
• falls on deaf ears
• fall through
• fall through the cracks
• fall through the floor
• fall to pieces
• false alarm
• false dawn
• false economy
• false start
• Familiarity breeds contempt.
• family man
• Famous last words.
• fancy-pants