The War of the Simpsons - S2-E20
Corrected entry: After Marge explains why they're having the party, Homer recalls their wedding very vividly, having, "priests, champagne, and musicians," but in Season 3, "I Married Marge," their wedding isn't that spectacular as Homer remembers.
Correction: Homer is an idiot, and his memory is not too good either.
SexyIrishLeprechaun
The mistake is valid, and not every mistake can be dismissed because Homer is an idiot sometimes. In the episode "A Milhouse Divided," he even wants to marry Marge again to make up for their cheap wedding at the chapel, which would not make sense if they already had a big wedding with champagne, musicians, etc.