It looks simple to me: that remark was not professional, it's something you'd say to a friend, ideally one with whom you share a relationship close enough to allow for remarks like that one. If you stick to professional interactions, you'll hardly create such a problem at a workplace.

The hardship begins when personal and professional relationships mix, but if a personal relationship is established it's reasonable to assume that both people should know how to deal with eachother and would have cleared this up between themselves. If HR was involved, it's because someone was out of line or just doesn't understand how adults manage boundaries, in which case he should be warned and, if the case merits, punished.