You oiled and then shaved دَهَنْتَ وأحْفَفْتَ.

دَهَنْتَ وأحْفَفْتَ.
يقال: حَفَّ رأسه يَحِفُّ حُفُوفا، إذا بَعُدَ عهدُه بالدهن، وأحْففته أنا.
يضرب للرجل يحسن القولَ في وجهك ويَحْفِر لك من خلفك.
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You oiled and then shaved.
It is said, "His head became dry," meaning it had been a long time since he oiled it, and "I made it dry."

This is said of a man who speaks well to your face but plots against you behind your back.
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المثل العربي «دَهَنْتَ وأحْفَفْتَ» يُضرب لمن يُظهر اللين وحسن القول في الظاهر، بينما يُضمر الأذى أو يعمل في الخفاء ضدك؛ فهو يلاطف بوجهه ويؤذي من وراء ظهرك.
وأقرب المقابلات الإنجليزية هي:
"He stabs you in the back."
«يطعنك في الظهر.»
أي يخونك أو يؤذيك سرًّا بينما يُظهر الود.
ومن الأمثال والتعابير الأخرى:
"A wolf in sheep's clothing."
«ذئب في ثياب حمل.»
أي يظهر الوداعة ويخفي الشر.
"Honey in the mouth, a dagger in the heart."
«عسل في الفم وخنجر في القلب.»
وهو تعبير قديم يقابل المعنى مباشرة.
"Fair words butter no parsnips."
«الكلام المعسول لا يصنع شيئًا.»
ويقال لمن يكثر من حسن الكلام دون إخلاص.
فإذا أريد أقرب مثل إنجليزي شائع يؤدي معنى المثل العربي، فإن أنسب مقابل هو:
"He stabs you in the back."
أما إذا أريد إبراز التناقض بين الظاهر الحسن والباطن السيئ، فـ
"A wolf in sheep's clothing."
هو الأقرب.
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The Arabic proverb "You flattered and then humiliated" is used to describe someone who outwardly appears gentle and kind, while secretly harboring ill intentions or working against you; they are friendly to your face but harm you behind your back.
The closest English equivalent is:
"He stabs you in the back."
"He stabs you in the back."
Meaning, he betrays you or harms you secretly while feigning friendship.
Other proverbs and expressions include:
"A wolf in sheep's clothing."
"A wolf in sheep's clothing."
Meaning, he appears gentle but conceals malice.
"Honey in the mouth, a dagger in the heart."
"Honey in the mouth, a dagger in the heart."
This is an old expression that directly conveys the same meaning.
"Fair words, butter, no parsnips."
"Sweet talk accomplishes nothing."
This is said of someone who speaks eloquently but without sincerity.
If you want a common English proverb that conveys the meaning of the Arabic proverb, the most suitable equivalent is:
"He stabs you in the back."
However, if you want to highlight the contradiction between a good exterior and a bad interior, then
"A wolf in sheep's clothing."
is the closest.