Why is it typical for spouses to rail on each other when the opposite spouse's parents/family are around?

Ive seen, heard or been part of many occassions when the parents or relatives of one spouse is in town and the other spouse gets hen-pecked or demeaned. What manifests this behavior?Why is it typical for spouses to rail on each other when the opposite spouse's parents/family are around?
When family is around people seem to change the way they act. I have noticed that this is true for both men and women and that attitudes change when both in-laws and blood relatives are around. I will use the wife for instance, her family is in town and suddenly she is giving her husband a hard time, it seems to me that she does that because she has a need for her family to see what she sees in her husband, and wants him on his very best behavior when her family is around. I think it's crazy though because if she would just let him be himself they be more likely to how great he his.





The other scenario is the wife's in-laws are in town and suddenly the husband is getting made fun of, all of his weaknesses are pointed out and he is completely derailed. Why is this? I'm not sure but I think it comes from a need to fit in with his family. I believe that some people feel the only way to show how well they know somebody is to point out all of their weaknesses. Chances are the family knows the weaknesses too and it gives them all something to laugh about, everybody but the husband anyway.