Back to the Future: The Game - 30th Anniversary Edition

This achievement occurs during Episode 3 - Citizen Brown

After returning back from the McFly household do the following:
• Walk over to the soup shop on the west side of town.
• Interact with Sign. (Sign below the counter, not menu sign.)
• Interact with Window.
• Dialog (Leech): "Free samples?"
• Dialog (Leech): "Never mind."
• to exit.
• Walk into the back alley.
• Interact with Ammo Box.
• Interact with Plank.
• Interact with Fridge.
• Use Item "Spray Paint" to equip.
• Interact with Plank (With Spray Paint equipped.)
• Exit the back alley.
• Enter the back alley.
• Interact with Plank
• Interact with Table.
• Use Item "Hotdog Sample" to equip.
• Interact with Einstein (With Hotdog Sample equipped.)

Credit to T_l_M_B_0 of PST

Chapter 3: Citizen Brown

Once you break into Hill Valley you'll learn about all the rules.

Go to the soup shop and ask for the free samples, this will trigger a cut scene with Einie. Go behind the shop and grab the spray can, use it on the plank of wood leading to the hole in the fence.

Hop over the fence and look for Einie, he'll run off.
Follow him and you'll lose him but he'll go back over the fence.

Simply hop back over the fence and follow his paw prints, give him a free sample, watch the cut scene and the 15 points are yours.