Meaning:
“四次元” means “four-dimensional,” and “人类” means “humans.” In the Chinese language, we use “two-dimensional” to refer to the world of games and animation, and “three-dimensional” to refer to real world. The concept of “four dimensions” is often related with the four-dimensional space-time continuum, which often appears in sci-fi movies or fiction and enables people to travel back or forward in time. Chinese netizens use “four-dimensional human being” jokingly to refer to those people who think out of the box all the time and come to conclusions different from normal logical thinking.
Example:
A: 为什么你妹妹生病了还很高兴？
Wèishénme nǐ mèimèi shēngbìng le hái hěn gāoxìng？
Why is your younger sister happy that she got sick?
B: 因为她是四次元人类，她觉得生病能让自己的免疫力升级。
Yīnwèi tā shì sìcìyuán rénlèi，tā juédé shēngbìng néng ràng zìjǐ de miǎnyìlì shēngjí。
Because she thinks differently from most of us. She thinks that an infection will upgrade her immunity.