I'm nobody.
我是无名小卒。
I'm somebody.
我是大人物。

chatty = someone who talks a lot
爱说话的人
Jack is a chatty person.
Jack是一个话很多的人。

messy = someone who is very untidy
I'm not a very messy person.
我不是一个不爱干净的人。
You are a compulsive cleaner.
你是一个清洁狂。
You are such a screen junkie.
你是一个玩手机上瘾者。

A couch potato is a lazy person who spends a lot of time sitting down or lying down, watching TV, playing video games, or doing some other activity that doesn't involve physical activity.
Couch potato指的就是很懒的人，成天躺着或者坐着，看电视，玩游戏，从不锻炼。
Jack is a laid-back person.
Jack是一个悠闲的人。
Mumu is an affectionate person.
木木是一个多愁善感的人。