the map must be goat bay.

tall goat is usefull.

please go straight to the cross road right in front of where you spawn.
there the helicopter will swoop by

you lick the helicopter when its near the ground.
it is there for a brief moment so you need good reflexes.
i got it no problem though so its not that hard

after you lick the heli in the crossroads you wait untill your goat is stationary above the skyscraper when the helicopter stops.

then if done right congrats you got yourself an achievement!
warning: don't go ontop of the skyscraper at any point. the achievement wont work if you or any other player in the game uses the elavator. if you do you must restart the level.