It's usually, "You can't fool me!" which means, "You can't deceive me," or it's, "Don't [even] try to fool me," which means, "Don't even think about trying to deceive me," i.e., "I can see right through your actions."
Also, "You fooled me!" means, "You tricked/deceived me." There are three different ways one could mean this:
1. I am in earnest, and you really deceived
2. Jokingly, as in, "You got me!"
3. Sarcastically to mean, "I don't believe you from your actions." Example:
Richard: Really, Yvette, I don't even like her, she's just a coworker.
Yvette: You sure fooled me [meaning, "Yeah right, jerk."]. I saw you give her a pair of diamond earrings.
There is also, "You could have fooled me," which can mean #3, or it can mean, "I woudn't have known the difference."
Jimmy: We had the best wine yesterday at a vineyard we visited. Really good quality, I think. Called "Beaujolais nouveau." Tasted like fine stuff. I bought some with the idea it will age well.
Jean: No, you'd better drink it now--it doesn't have the best reputation--and it certainly won't age well!
Jimmy: Oh, could've fooled me--I don't know anything about wine.
Hope this is clear. Other Anglophones feel free to fine tune.
"You fool me" can be used as in "If you fool me once, shame on you, if you fool me twice, shame on me". That's a common little saying but I would only use "you fool me" only if I was repeating it. I wouldn't use it in conversation.
Where on earth did you come up with "don't fool me!" and "you fool me!".
Can you prove they came from native speakers? If so, where?
"Don't fool me" looks like it started life as either "don't try to fool me!", in which case fool means deceive; or the very idiomatic "don't fool with me!", which has at least two meanings: don't try your luck against me; don't waste my time with your distracting remarks or actions.
"you fool me!" most likely started life as "you fooled me!"