the sound a car makes when they are gonna get tf outta there so skrskr means your gonna get out there quick as a bitch, usually used as a term you say with your friends though as a joke.
The phrase your friend keeps shouting when you are walking to town to buy some food and you really want to tell him that the hip-hop he listens to is crap and skr skr means nothing.
When you speak to a friend, you might say this. It is something you say casually as a greeting or a way of showing you are good friends. It expresses your mood, most often happiness and chill-ness. Most of the times it is randomly said as nice premium banter.
Joe: Suh dude!
Rob (Hip af): skr skr
Joe: haha your so funny!