5 Seconds of Summer Bass Player Cops to Flashing Dong around The Web

5 Seconds of Summer's Bass Player

5 Seconds of Summer's bass player now has a viral penis -- which isn't as bad since it sounds -- but yes ... his junk's being passed all around the Internet after he flashed it on Snapchat.

Calum Hood learned a tough lesson (pun intended, we have seen the video) when he sent the revealing video to somebody who then reposted it as a Vine to share with the world to see. So, now ya know, Calum -- famous naked penises Keep getting leaked.

Even though you never see 18-year-old Hood's face within the video ... he took the brutally honest step of admitting it was him by tweeting ... "I'm still just a teenage kid learning from mistakes ;)"

So, he's young, dumb, and ...