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1.
A word that describes the manner in which someone reacts.
Similar usage to "frog in a sock"
She doesn't look flash but I bet she goes off like a fish milkshake

by Japanese Maths September 07, 2006
 
2.
Lesbians (preferably good looking ones like in the movies) going down for the growl on each other (usually 2 good looking lesbians but the more the merrier)preferably at the same time (69er), or a guy going down on a chick.
Check out those 6 good looking lesbians eating each others wet juicy pussies, judging by their smiles they must be enjoying their Fish Milkshake.
by Jimmy B from Oz December 21, 2009
 
3.
an early 'engineered' functional food, product of the Captain Curd Company ... Wollongong, Australia (c. 1974)

research continues at the University of Wollongong
Fish Milkshake, Why don't you try the new taste sensation plucked from King Neptune's depths and brimming with bovine goodness? When you wake up in the morning feeling RS, come on down to the canteen and try the marine flavoured dairy product, Captain Curd's Fish Milkshakes. Remember Curd's rhymes with Birds.
by bogun5000 February 17, 2011