yes,the anserabove are correct,and there also imply the woman is nice,especially good looking*__*

That means some aspect of man is much lower than the woman, such as features, education, style, social class, money, age or other like this. All in a word, this is means the man is much bad to match the woman.

一朵鲜花插在牛粪上 - the direct meaning to the chinese concept is a beautifuy girl married to an ugly guy. But the true concept in this expression is an implication of jealous of that man who have a beautiful wife. The expression is offensive which is used to insult the man. There are two different meaning between the speakers and the listeners

Arabella is right. It doesn't just mean the man is old or disgusting. The phrase emphasize they are not match. Since it's derogatory sense, don't say this phrase to a man who is not a bad or disgusting guy, just some such as features, education, like Arabella said, does not much the woman.