When two midshipmen get "involved" with each other. similar to darksiding.
"MIDN Ay hooked up with MIDN Bee last night and now the whole platoon knows about it. I told her not to get involved in any midcest."
"mid"shipman in"cest"; a slang term for the act of a mishipman getting "together", personally or sexually, with a fellow midshipman from the same unit/school; usually used by any military unit that is training midshipmen such as the Naval Academy or Navy Reserve Officer Training Corps (NROTC).
Gunnery Sergeant: There will be no midcest whatsover going on in during this training, do you understand!?