The present article deals with an Arabic-Hebrew Geniza document found in the Heidelberg papyrus collection. The recto and part of the verso of the document contain an undated letter by an Egyptian Jew living in the 11^th/12^th century ad, addressed to a co-religious fellow. The letter is not only unusually impolite but also linguistically exceptional as it is written in Arabic language and script with interspersed Hebrew elements written partly in Arabic and partly in Hebrew script. The verso of the document also displays several parts of a love poem by Yehuda Halevi in Hebrew which do not belong to the letter but were added by the addressee or another person not identical to the writer of the letter. The article focuses on the linguistic and epistolographical features of the letter and its cultural background on the basis of an edition on the one side and presents an edition of and commentary on the poetic fragments on the other.