I'll never understand it either. The biggest problem with it is more than one mother-in-law. ROFLMFAO!!!!!!
Fortunately, I lucked out. My mother-in-law and I get along very well. We've gone to bars, we've gone to Phillies games, we watch sports together. Having said that, she's a Mets fan, and wanted to kill me when the Mets choked (twice) to the Phillies in the NL East.