When I find myself in a situation where I question whether an expression translates literally, there are a few ways I proceed.
Check the origin of the expression. Often times the phrase is from an internationally known work and the phrase is more international than you'd think.
Look for explanations or synonyms of the expression and try to translate them.
Check to see how the phrase is translated into other national languages for inspiration.
The phrase, the best I can tell, dates from the mid 1900's - but not from any internationally known source that I can track down. (One can't help but wonder how we expressed the idea in English before then and whether that expression would be helpful in this discussion.)
The second option turned up the following:
- To pretend to be uninterested in a romantic relationship.
- Pretend to be inaccessible or uninterested;
- act coy, especially with the opposite sex.
The first choice suggests Andrew's ŝajnigi sin neinteresata. "Coy" is often translated modesta, sinĝena, or retiriĝema -- of these three I think sinĝena is the best choice.
I found some interesting expressions in French and German. The most transparent of them was the German sich unnahbar geben - sin ŝajnigi neatingebla.
Of all the possibilities suggested or considered so far, I would consider sin ŝajnigi neatingebla the best choice, both for this context and in general.