Loss of words
A phrase used as an excuse to not say anything. Typically used to politely not talk to "friends" you actually don't want to be friends with.
Example:
Person 1: Why don't you ever talk to me anymore? Do you not want to be my friend?
Person 2: Sorry, I've been at a loss of words lately.
Person 1: Why don't you ever talk to me anymore? Do you not want to be my friend?
Person 2: Sorry, I've been at a loss of words lately.