to fly in the face of logic

to fly into a passion

Go fly a kite!

fly in the ointment

flying at maximum altitude

We're flying across the Atlantic.

foam at the mouth

to foam at the mouth

to foam with rage

to be foaming with rage

to fob someone off with promises

to fob someone off with something/to fob something off on someone

to focus on

in a fog

fog and mist

It's foggy.

to fold away

to fold one’s arms

to fold one’s arms around someone

to fold one’s legs

to fold someone in one’s arms

to fold up

to fold up papers

Hi, folks!

folks