25-year-old Arnette -- a 1st round draft pick -- was arrested on Friday, January 28 on Las Vegas Blvd. after cops received a call about a man who allegedly pulled a gun after becoming irate with a valet at the Park MGM resort.

Las Vegas Metro PD say they located Arnette driving a black G-Wagon around 6 PM on Las Vegas Blvd. When they pulled him over, they say they located two guns in the car. One of the weapons was found on a passenger (a Glock 36), and the other was found next to where Damon was seated.

As for the incident that led to the arrest ... a Park MGM employee said he retrieved a prompt to retrieve the Benz. However, when the valet delivered the car, he asked to see Arnette's ticket -- which he said he'd lost. That's when Damon allegedly lost it, yelling "give me my mother f***ing keys!"

Shortly after the valet says things took a turn for the worst. The male employee claims he heard a gun cock, and when he looked up, Arnette was pointing the firearm at him, and again demanded his car.

Arnette eventually got his keys and left ... and police were called. Damon was pulled over and arrested shortly after.

Police say they viewed surveillance video from the casino ... and the video shows Arnette "took a handgun that was concealed from his pants and placed it in the drivers side interior door."

Police say "it appears that Arnette gets irritated and starts yelling at the attendant."

The argument continued, and LVMPD says "Arnette then appears to reach down and charge his pistol using both hands."

FYI, to charge a handgun is to cock the handle.

It gets worse for Damon. Police say they found 3 baggies of cocaine -- totaling 1.8 grams -- in his pocket. They asked Arnette about the powder, and he told them it was ketamine, but that it was not his.

Cops say they also located 13.5 ounces of what appeared to be marijuana (the alleged weed hasn't yet been tested). LVMPD says Damon admitted to having a large amount of pot in his car for personal consumption.

Arnette was eventually booked on 4 felony charges including carrying a concealed weapon, assault and drug possession.

It's not the first time he's been in trouble. Arnette was cut by the Raiders after a video surfaced where he appeared to threaten someone with a weapon.

Arnette is also being sued for an alleged hit and run where someone was seriously injured.