This achievement occurs during Episode 3 - Citizen Brown
Assuming you have collected your Guitar from the McFly house do the following:
• Walk over to the soup shop on the west side of town.
• Walk into the back alley.
• Interact with Jennifer.
• Dialog (Jennifer): "You and the SoupMo guy?"
• Dialog (Jennifer): "Guitar? I play guitar!"
• Dialog (Jennifer): "I can outplay Leech any day!"
• Dialog (Leech): "Scissor Kick."
• Dialog (Leech): "Move towards Jennifer." (You may need to move toward amp before this option is available.)
• Dialog (Leech): "Climb on platform."
• Dialog (Leech): "Hop" (If this option is not available, you will need to select Climb on Platform again.)
This scene plays differently depending on where Leech moves to, you goal is to get Leech to stand on the plank which is laying over the dumpster which he will only do if hes near the boxes on the floor it and you are near Jennifer. Once in position hop and Leech falls in. After the cutscene you will be kissing Jennifer, in order to get caught you need to:
• Interact with Window
Edna will catch you and the achievement will pop once Officer Parker walks off
Credit to T_l_M_B_0 of PST