EXCLUSIVE

'Buffy the Vampire' star Nicholas Brendon should stay far far away from geek conventions because it never ends well ... he was arrested AGAIN in Florida Friday night.

According to a police report, Brendon called cops reporting his phone and wallet had been stolen. When officers arrived they saw Brendon had flipped his bed and over-flowed the toilet in his room. He had done other things to himself suggesting he wasn't of right mind. As for his wallet -- it was on the dresser.

The report states that hotel employees told police Brendon had been mixing pills and alcohol at the hotel earlier in the day. Officers discovered a pill bottle that was filled with 10 pills earlier in the day only had one remaining.

Brendon was in town for ALTCon, a pop culture convention.

TMZ broke the story ... the actor was arrested in February for a similar drunken hotel incident ﻿at the same time of convention. He did $450 worth of damages to a room and refused to pay his $380 tab for food and beverages.

And Brendon was busted in October after an incident in an Idaho hotel lobby when he got into it with guests and staffers.

He clearly needs help.