Alright, both of the crank arms were coming loose pretty frequently. And I've read NDS crank arms are the first to go.
Just stopped by my friend's and popped off the NDS crank arm. Looks absolutely perfect. Didn't even feel the need to check Drive-side as there would be no reason for the NDS to be perfect and the Drive Side to be destroyed.

Must've been that Shimano bottom bracket.. or the old crank bolts I just replaced with 8MM Hex Shimano ones.. Weird.

Either way, stoked.