How old is your son and did he actually cry? I had a similar situation with my parents a couple years ago(though I wasnt nearly as bad as your son) and when they started doing the stuff you did we started a friendly one-upsmanship contest but I lost by putting tabasco, hot chili sauce and lemon juice in my dads marmite sandwich.....only thing was the bastard actually liked it and asked what I did to the sandwich to make it taste so good so I gave up. Shoulda figured a guy that eats marmite sandwiches wouldnt be phased even if I put dog crap in his sandwich.
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I am ken BOW TO ME!