First, you must be drunk to perform the sonar slide. Then you have to find a girl and fuck her in the butt with her forehead on the ground. Right when you skeet you throw up down her back, yell "SONAR SLIDE" and grab your clothes and run.
Yo man I was so wasted last night that I sonar slide'd a girl. She was so pissed I had to run out of the room with no clothes on.