Sometimes, we think someone is a funny guy because of who did something intresting. You may discribe that he is a 活宝!!It's not a disrespect word, so don't worry about it.
There is another aggressive word "笑话".When you use "笑话" to discribe a guy, which means you don't like this guy at the same time.
To sum up,
He is a 活宝=> no disrespect, to use to discribe some one behave funny.
He is a 笑话=>paying no resprect, to sue to discribe some one as a joke.
ex: John 好搞笑,他真是个活宝!!大家都很喜欢他. like him.
ex: John 好可笑,他真是个笑话!!大家都很讨厌他. dislike him.