Play video content EXCLUSIVE 02/15/18 TMZ.com

Lil Pump isn't taking his arrest Wednesday night seriously ... which is the biggest understatement of the week.

We got the 17-year-old Thursday at 2:30 PM leaving Sylmar Juvenile Court, and he was as hyped as ever, showing off his newly acquired jewelry ... an ankle monitor.

He was also spittin' bars about popping Xanax and boasting about Gucci tats.

TMZ broke the story ... Pump was arrested for firing a handgun into the door of his San Fernando Valley residence. He had told cops intruders had fired from the outside in, but cops quickly realized it was the opposite -- that Pump was the shooter and there were no intruders.