I went to dinner with two idiots, Donald Trump and Joe Biden.
Vs
I went to dinner with two idiots, Donald Trump, and Joe Biden.
If you intend for the reader to think you went to dinner with two people, treating the Oxford comma as mandatory is going to add ambiguity at best and change the meaning at worst.
When it changes the meaning.
Vs
If you intend for the reader to think you went to dinner with two people, treating the Oxford comma as mandatory is going to add ambiguity at best and change the meaning at worst.