when the upper front of a woman is shaken vigerously in a male or females direction to catch their attention. usually done to a very fast beat. sometimes (if the females are competitive) they will have a milkshake competition to see who can milkshake the fastest to get the most attetion.
man i was in a trace when my girlfriendmilkshaked in front of me. then a saw her later, milkshaking to my best friend so i went to her best friend and she also gave me a milkshake which was way better than my girlfriend.
in the kelis song ''my milk shake brings all the boys to they yard.'' it really means her blow job brings all the boys to the yard coz milk shake is when a girl give u a blowjob u gets the cum and froths it up in her mouth meaning milk shake