ThornyThorny literally describes plants like roses, that have sharp pieces called thorns. You can use the word figuratively to describe something that is troublesome, difficult or stressful. It is often used with the word issue, as in a thorny issue, meaning a situation that is stressful or difficult to talk about.
EX: Education policy is a very thorny issue in our family. My sister is a teacher so she definitely has her own perspective on it, but my dad is a convinced conservative and he supports a lot of harsh market reforms. They argue constantly.
EX: The police brutality case is a very thorny one in our city because it involves serious charges of racism. The race relations here have always been complicated.
To remind us that even good things often have their disadvantage, you can say the expression every rose has its thorn. Something or someone that is really annoying and won't go away is a thorn in your side.
EX: The weather in Granada is wonderful in spring and it's sunny pretty much all year round. But every rose has its thorn, and in the summer months it can be unbearably hot there.
EX: My sister Sarah is nice, I love her and everything, but she can be a real thorn in my side at times. You know, she's pretty socially awkward and always wants to leave a party just when I'm starting to have fun.