竹を割ったよう is an interesting phrase, it literally means “like or similar to split bamboo.” When we use it in Japanese though, we use it to express a person with a straight forward personality, or someone who is direct and to the point. Directness and bamboo don’t immediately seem related, so what is the connection here?
Bamboo fibers run vertically, so when we slice bamboo with a knife, the bamboo splits very easily and cleanly. When we use 竹を割ったよう to describe someone’s straight forward personality, this is the metaphor we are trying to create. Also, the inside of bamboo is empty, which also represents the idea of someone having nothing to hide. Therefore, if we describe a person as 竹を割ったよう, the person is not only straight forward, but also honest, frank, and open hearted.
竹を割ったよう has a very positive connotation and can be used as a compliment - so feel free to use it to describe your friends! But note that 竹を割ったよう is really only used to express person’s personality. It doesn’t make sense for us to use this expression for the other things which are “straight forward”, such as a “straight forward question” or a “straight forward direction”.
竹を割ったよう works as な-adjective, and is very often seen combined with two other nouns. The first is 性格 (“character / personality”) - for example, 竹を割ったような性格. We also see it used often with 人 (“person”), like 竹を割ったような人. When using it with 性格, some people even omit the ような and abbreviate the phrase by saying 竹を割った性格. But be careful - you can’t really do this 人 and say 竹を割った人 - this is confusing because it sounds like “the person who cut the bamboo”. Make sure to use the whole correct phrase when using 人 in your sentence!
My boss is a straight forward and frank person.
Because he is a straight forward and direct guy, even he gets angry, he forgets about it quickly.