What goes too far in terms of "pervy content"?

If a picture doesn't show actual nudity or sexual content, but shows something that could be considered perverted (or ecchi), how is it judged?

For instance, I know of a 4-koma comic where several of the League women are at a hot tub, and Lux is envious of the breast sizes of the others (whereas she is flat). While the women are clearly unclothed, nothing explicit is shown. Does this cross a line?

Just trying to get some clearer outlines for this rule.