Stu's shirt collar disappears when he's driving home.
When Grandpa Lou first looks at the prize section for the beauty contest, the "Dads! Win!!!" text is red, but when he shows it to Stu, the text is black.
When Grandpa Lou shows Stu the newspaper about the Kingfisher 9000, his head vanishes.
There is no need for Tommy to wear a wig to look like a girl, lots of baby girls are as bald as he is.
The entire plot line of Tommy being disguised as a girl and entered into the beauty contest would have been avoided if Lou had realized early on that Angelica, his other grandchild, could enter the pageant legitimately.
Somehow, Didi is the only family member who knows about Angelica being in the pageant, and attends in support of her niece alongside Drew. Stu and Lou only find out about the pageant through an ad in the newspaper and are surprised to see Angelica competing later on when they enter Tommy (as "Tonya") in the pageant. Angelica's entry into the competition should have been big news shared with the entire family (including the as-of-yet unseen but mentioned Charlotte, Angelica's mother), not just Angelica's father and aunt. One way or another, Stu and Lou absolutely would have found out about it at some point before that day.