还可以。

You can use it as a standalone answer or at the end of a sentence. If someone asks how your dinner was, just say 还可以. If you want to describe a movie, you can say 那部电影还可以. It functions as an adjective meaning 'okay' or 'decent.' It is very easy to plug into conversations because it requires almost no complex grammar. Just drop it in whenever you feel 'meh' or 'fine.'

Use it when you want to be polite but honest. At a restaurant, if the food is good but not life-changing, use it. When a friend asks about your new job, and it is just okay, use it. It is perfect for texting when you are in a rush. It also works great in business meetings to give a neutral status update. It keeps you from sounding too negative while staying grounded.

Do not use this if your best friend just got married or won the lottery. Saying 还可以 to their big news will make you sound like a cold-hearted robot. Avoid it when someone puts in massive effort for you, like a five-course home-cooked meal. In those cases, use something more enthusiastic like 太棒了. Also, if your boss asks if you finished a critical task, don't just say 还可以—be specific!

Chinese culture deeply values the 'Middle Way' or 中庸. Being too loud or too boastful is often looked down upon. By saying 还可以, you are practicing a form of social safety. It protects you from being wrong. If you say a movie is 'the best ever' and your friend hates it, you look silly. If you say it is 还可以, you are safe. It is the ultimate shield of social harmony.

You will often hear 还行 (hái xíng), which is the more casual, 'cool' younger brother of this phrase. There is also 还不错 (hái bù cuò), which literally means 'not wrong' but actually means 'quite good.' If you want to sound even more casual, you can just say 还可以吧, adding that 吧 at the end to make it sound softer and more like a question.