the fat hit the fire
The point at which a situation abruptly, and perhaps drastically, worsens. Mom already seemed annoyed, but the fat really hit the fire when she found out that you'd been lying to her.
*fat hit the fire
Fig. a situation that suddenly becomes frantic and unpleasant. (*Typically: suddenly ~; then ~; when ~.) Things were looking bad in the stock market, then the fat hit the fire and I lost everything.