Definitely the most common reason posts are removed. Nudes are cheap, this sub requires some creativity.

The full text of Rule 2: Overt nudity not allowed

Aim for very titillating and sexual without showing any overt nudity. Nipple exposure is permissible, but full breast exposure is not. Subtlety is key! The subreddit is about sideboob, not full boob. It is up to the discretion of the moderators as to what is acceptable.

Topless and from the side or behind is still considered nudity. Topless with a hand covering is still nudity (try /r/handbra). Moderator discretion applies.