Meaning of lose your rag

[Veki]

Test No. incompl/inter-62 "Losing It (2)", question 4

First he started shouting and then he began to throw things round the room and it was clear he had just lost his ..........

(a) rag
(b) cloth
(c) cover
(d) sheet

Test No. incompl/inter-62 "Losing It (2)", answer 4

First he started shouting and then he began to throw things round the room and it was clear he had just lost his rag.

Correct answer: (a) rag
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Please answer me.
I can guess what means "lost his RAG" but I can't be sure.
Thank you.

[Alan]

This means lose your temper/lose control of yourself.
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English as a Second Language
You can read my ESL story Adverbs