I tried actually counting them. My past 80 comments (not counting recent ones just now) have all been modded down at least once. There are some that are at 0, but only because another person modded them up as well.

(I tried counting before and found the 54th comment was not modded down but I can't seem to find that comment again, for some reason.)

This covers well over the whole month. I'm still at positive for the month because I have enough upvotes on my comments that voting each one down by 1 still leaves me at positive.