'*Sigh* Sadly I can't make a move on him or I would offend the big guy up there.'
Karna badly wanted to pull something to take care of Narada as Karna know how dangerous this man could be.
This is a man who made a fool of a wise and intelligent man like Ravana, Same guy also convinced the Kansa to kill literal new born babies, So this guy is danger no matter how one look at him.
But Karna can't touch Narada at all. How can one be hurt a person whose father is the god of creation and lord is the god of preservation? It can't be possible unless other party also have the same level of support.
Sadly for Karna he didn't have that extent of support yet, He knew how good Lord Vishnu is towards his devotees and mankind, If he felt others were threatened by his power then Karna didn't have anywhere to cry.