Could you tell us the nuance of this expression? How can I use it in other situation?
Native speaker’s answer
Rebecca
Here, "I'll tell you what" is an informal expression that is used to introduce a suggestion. Chandler says "I'll tell you what" and then suggests that he and Joey spend more time together. Ex: I'll tell you what. Why don't we start working out together? That way I can help train you. It is also used emphasize a statement that will follow. Ex: I'll tell you what. He seems strict but he's actually a really fun guy.