There is no official slang term for DSF. However, those 3 letters are located next to each other on a keyboard. It is likely that a person will accidentally type the 3 together in a message or text, thus causing confusion on the receiving end of the message.
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dsf dsf
If you mean slang as in internet slang, then it means "Certified Old Fart".
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$2.19
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Slang is slang It's the s' "LANG " uage.
In old slang, milkshake mean butt.