Lose the plot 

To stop acting rationally.

The day of her wedding, I thought Amy was going to lose the plot.

Lose the plot by Tige Gentry July 23, 2006

Lose the plot 

Get really angry and lose your self-control. Derogatory, as implies that it wasn't a reasonable reaction in the circumstances.

After Dad saw my picture on the front of the porno DVD, he completely lost the plot.

Lose the plot by Observer52 September 6, 2005

Lose the plot 

To lose the ability to cope with or understand what's going on around you.

Feminist Frequency is complaining about lack of diversity in female character designs in OverWatcth, a game that went out of its way to have the most diversity in female character designs. Way to lose the plot, Feminist Frequency!

Lose the plot by JohnSmith1495 September 3, 2016

Lose the plot 

To lose all self control and go absolutely bonkers. Make stupid and irrational decisions. In most cases only lasts a few minutes but sometimes can be permanent which will require long periods of habitation in psychiatric hospitals with the men in white coats.

Jimmy will lose the plot when he finds out someone stole his New Kids On The Block album.

Lose the plot by Limbodancer November 7, 2018