You earn Ventkids standing by doing tricks on your K-Drive. You earn 1 standing for every 4 points you score from those tricks. The most points you can earn in one trick is 3000, meaning 750 standing.
I found a way to consistently score 3000 point tricks in significantly less than a minute. Find a nice flat place away from enemies (like one of the lakes), and be in boosting mode on your K-Drive. What you want to do is mash the jump button as fast as possible while moving the left stick in a circle. By mashing the jump button, you will be both performing tricks while in the air, then jumping immediately when you land. If you jump fast enough, your trick does not end and will continue earning a multiplier. Once you try for a little bit you should get the hang of how to do it. I tend to stop the trick at about 80 points, with a 40x multiplier (3200 points).
Here is a video example:
Sorry, this Game Clip has been removed
EDIT: seems to have been patched as of 3/20/19