Plot hole: Janet and Chrissy accuse Jack of making the fake BBQ telegram. However, Jack was at The Apartment the whole time, never left once until after he found out Lori was the one who made the telegram. If it was Jack who made the fake telegram, he would have had to leave The Apartment to do that.
Suggested correction: True, there's no logical way that Jack could have sent the telegram. But Janet and Chrissy were upset about it - when someone's upset, they don't always think in a logical way.
Or he could've called Larry and had him set it up but I don't think he ever used the phone to call anyone.
Plot hole: At the party, when Jack tries to suddenly stop many guests from eating his tainted cake, he knocks away the cake from many people to prevent them from eating it - but at least two minutes or so have gone by since the guests were given the cake slices so most likely, many (if not all) the guests would have tried the cake within those two minutes. And yet somehow Mr. Roper was the only one who is revealed to have actually tried the cake in all that time.