How do you know a hippie is on her period?
Her socks are missing.
How do you know she's off?
Her socks are tye-dye.
How do you know a hippie is on her period?
Her socks are missing.
How do you know she's off?
Her socks are tye-dye.
This is a silly play on words. The joke plays on the idea that during menstruation, women might misplace things, and then connects that to the association of tie-dye with hippies. It suggests that once the period is over, the hippie has recovered all of her tie-dye socks.