"I painted a room and had to pop out the light switch plate (no screws, it was just pushed into the wall), it should just pop right back in when I try right?
No matter where I try to apply pression it doesn't stay in it's place, there's no obstruction that I can see, I didn't even move it that much to paint around it, but I feel like I'm missing something."
Does it not stay because it doesn't fit back into the opening now, or does it fit then slip back out? If it's the former, the cwm 's idea is the first thing to try. If it goes into the opening that it came out of but won't stay put, it could be that pulling it out widened the opening, or if you used a high gloss or oil based paint, there might be less friction. Also, if you pulled the switch itself out the wires behind it will unfold a bit, and if they're not refolded they might be preventing the switch (and thus the plate) from reseating the way it was. And to ask the obvious question, is there a reason why you can't put the screws in it to keep it in place? If there is, then you might want to use some sort of adhesive to stick it back in place, but the switch should really be attached to the box for safety reasons and the plate could then be screwed to the switch body.