Looking for a word that describes the feeling of being told something in an overly simplified manner that feels offensive.
- to adopt an air of condescension toward : treat haughtily or coolly
to behave or treat in a condescending way
The adjective form of this would be patronising.
A professor who patronises his students would be someone who acts as if their students are very young.
- showing or implying a usually patronizing descent from dignity or superiority:
They resented the older neighbors' condescending cordiality.
This comes from the verb to condescend:
verb (used without object)
- to behave as if one is conscious of descending from a superior position, rank, or dignity.
The phrase that will work best is:
Talk down to
- to speak in a condescending or oversimplified fashion
If you wanted to use a single word, this one may work, depending on the context:
- to cause (a person or thing) to seem little or less; talk down
eli5 is a phrase that is used a lot on reddit that means basically this