18w30a added support for forcing a JVM crash with Control+F3+C. However, this doesn't appear to actually work; holding left control and pressing F3+C never triggers the countdown, and pressing control after the countdown starts just causes a regular crash.

Curiously, right control works, for unknown reasons; the code uses GuiScreen.isCtrlKeyDown which checks both left and right. It's not related to keybindings, as it happens even if sprint is rebound to another key.