I've learned that "You're a fine one to talk" is synonymous with "Look who's talking".
Could you tell me the meaning of "fine" and the construction of the phrase, especially the usage of "to"?
I'd say it meant 'You are in a good position to talk'.
So I'd say that the to talk is a final (purpose) construction.
You are the one to do something; you are the best person for doing something; you are a good person to talk; you're a fine one to talk.
Both are used sarcastically.
Awho is well known for being corrupt) Let us make sure that the guilty are made examples of.
B: Your a fine one to talk, you were the first to sell out to the enemy.
I've learned that "You're a fine one to talk" is synonymous with "Look who's talking".
Could you tell me the meaning of "fine" and the construction of the phrase, especially the usage of "to"?
We could try to analyse this question till the cows come home (fixed expression, means for a very long time). But since "a fine one to talk" is never used except after the verb to be, and always with exactly the meaning you've guessed, it might be simpler to remember it as another fixed expression and leave it at that.
(And if you're going to ask me which cows, and where they're coming home to, I'll give the same answer. )