It's often used in a humorous or lighthearted way, especially online.
Here are some examples:
* "Me wow, that cake looks amazing!"
* "Me wow, you finished that marathon in under 4 hours!"
* "Me wow, that's the coolest new gadget I've ever seen!"
The expression can be seen as a modern, informal way of expressing the same sentiment as "Wow!" or "That's incredible!"