A person was discussing his mood swings. This is a nice congruent conflation of “flip-flop” and “turn on a dime”, both meaning to change direction quickly. “Flip (or toss) of a coin” (randomly) might also be in the mix given the words “of a”, and the mental image of someone flipping a dime might have entered in the speaker’s head. As I have mentioned in previous posts, dimes seem to show up a lot in malaphors, possibly due to their use in various expressions – “turn on a dime, “stop on a dime”, “dropped the dime”, “get off the dime”, “nickel and dimed”, etc. Some previous posts include “I fall asleep at the drop of a dime” (https://malaphors.com/2014/06/26/i-fall-asleep-at-the-drop-of-a-dime/) and “you had to figure out what to do on a dime’s notice” (https://malaphors.com/2014/05/20/you-had-to-figure-out-what-you-were-going-to-do-on-a-dimes-notice/). A tip of the toque to Martha Fenimore for hearing this one and sending it in!