a sore point
A topic that makes one angry or uncomfortable. Whatever you do, don't mention his ex-wife—his divorce is really a sore point with him.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
a sore pointor
a sore spot
COMMON You can say that a subject is a sore point with someone or a sore spot for them if it makes them feel angry, embarrassed, or upset. The continuing presence of foreign troops remains a very sore point with these students. Slow job growth is a sore spot for the US President. Note: If you touch or hit someone's sore point or sore spot, you mention a subject which makes them feel angry, embarrassed, or upset. The mention of Jim Kennerly had touched her sore spot. It was clear by his expression that my question had hit a sore point.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012
a ˌsore ˈpoint (with somebody)a subject or matter that makes somebody feel angry or hurt: The tax increases are a sore point with Jake, as he’s going to lose a lot of money.
Farlex Partner Idioms Dictionary © Farlex 2017