“You seem forced” can be used to indicate what you’ve expressed
Your meaning may have been gotten better than you think. “You seem forced” employs a fairly common usage of “forced”, indicating strain even though there is not a physical force. Note that “you look forced” in your question’s title is a little different, having to do with the way that “seem” refers more comprehensively to apparent behavior and “look” refers more to physical appearance.
Another way to say this that would be specific to tone of voice, diction, etc. would be “you sound forced” which could be hedged a little as “you sound a bit forced” and would be helpfully followed by a bit of explanation or a question, such as “is everything OK?”¹ or “do you feel you have to talk to me?”
Expanding on the “look”/“seem” difference in “you don’t look yourself”
With “you don’t look yourself”, it seems like you are saying that something about the other person’s physical appearance is unusual compared with historical data or some assumed expectation (e.g. someone’s face is green or streaked with tears and you assume they are not always that way, even if you don’t know them).
If you were to say “you don’t seem yourself”, your comments would be understood to refer to someone’s overall presentation. This could certainly include physical appearance, but is more often used to refer to someone’s speech, body language, and other aspects of behavior. I believe this phrase would fit the situation you described.
Note for “you don’t seem yourself”: Similar to “you don’t look yourself”, you would be understood to either be making a comparison to ways you’ve seen this person act before or ways you assume they normally act. For example, you think that the person doesn’t normally put so much emphasis on their words or deliver them in a staccato rhythm.
The note from the end of §1 of this answer applies here as well. Since you’re guessing at something about another person, it probably wouldn’t be a bad idea to describe a little more what you mean by what you’re saying. I personally think it would be appropriate to ask a question aimed at learning more about how this person is feeling and/or what they think about the situation.
“That is typical of you” is exactly what “You would!” means in this context. It is listed in some dictionaries, though it can be a little hard to find among the many other meanings of would; for example Cambridge lists it as
would modal verb (FREQUENCY)
(…) disapproving used to suggest that what happens is expected because it is typical, especially of a person's behaviour:
"Madeleine called to say she's too busy to come." "She would - she always has an excuse."
This is closely related to the meaning explained just above: would can express something habitual. For example
He would always turn and wave at the end of the street.
means the same thing as “He always turned and waved …” but the use of would stresses the fact that it's a habit.
As for what you read in Urban Dictionary — don't mistake UD for a useful reference. A lot of what it contains is just what one person decided to add and doesn't mean that anybody else would understand. I, for one (admittedly not a native English speaker), have no idea what why “you would” is supposed to be annoying or this “I did forget”/“but really” business is supposed to mean (maybe it implies that “you would” was used sarcastically?).
Best Answer
The usual wording of this idiom is "the pot calling the kettle black". The idea is that the pot is black itself, so it is not in the position of being able to accuse the kettle of being black. A very similar idiom you will probably be familiar with is "he who lives in a glass house shouldn't throw stones [at others]", or any variations thereof. Wikipedia has more similar idioms still.
The pot-kettle situation is a shorthand to refer to that idiom. It is not a common shorthand, so you won't find it in a dictionary. It is just a hint by this particular author at the actual idiom.