INTELLIJ YOU PIECE OF SH*T, I CLICKED "SMART CHECKOUT" NOT MERGE 2 UNRELATED BRANCHES, SCREW UP MY MASTER AND DON'T LET ME RETURN UNTIL I FIX ALL MERGE CONFLICTS.

Git merge --abort?

Seriously man, don't use the inbuilt VCS handling system. Use command line/GitKraken. Anything but the inbuilt one!
IntelliJ is amazing in all aspects, except for VCS integration. I noticed a serious 50% increase in the performance by disabling VCS in IDEA. It seems to constantly run the diff algorithm when you write code to an already existing file. It getting frustratingly slow sometimes!
Or ya know.. Maybe my PC is a bit sub-par compared to the pros.

Oh yeah, what a bad name for this function. Why it doesnt allow me to mark just the files that I want to stash, it also merges it to the next branch?? WTF? Anyway, you can apply git reset hard, this will delete any uncommited changes to the branch, because the uncommited changes are stashed on the original branch, but better check it beforehand! I then run into an issue with zombie files that git sees but aren't there! So, lesson learned dont use smart checkout!