GUYS:What would make a girl unforgettable?

This question is for for guys in general,but ladies can also answer if they would like.What makes a girl unforgettable,what has a girl done for you to make her unforgettable,or what does a girl have/need to do to make her unforgettable?Please leave your age if you can and thanks :)
Update: By "unforgettable" I mean that after months,weeks,days,or even years after seeing/talking to her,you remember her every now and then.In a GOOD way.
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