Courtesy Spencer Pratt
July 14, 2010 01:00 AM

There was already speculation Spencer Pratt would attempt to crash the party for the surprising series finale of the show that made him famous – and to his credit, his unwelcome presence throughout Tuesday’s Hills festivities did not go unnoticed.

Pratt, who was denied a room at the Roosevelt Hotel where the main events for the evening took place, did not let that stop him from making his way into the Hollywood hotspot. “When he couldn’t get a room,” a pal of the reality star tells PEOPLE, “he a had a friend of his book a room under their name instead.”

While his estranged wife Heidi Montag was nowhere to be seen, Pratt, 26, apparently wanted his own version of a reality show: An eyewitness tells PEOPLE friends were filming him with a hand-held camera as he crept around the vicinity.

“He walked in through the valet and up into an elevator with a small group of friends,” the source says. “He was dressed in an all-black suit, with hair slicked back, sporting a handlebar mustache curled up at the sides. He was carrying a huge hiking backpack and ranted as security guards from the hotel tried to figure out what to do. But once he made it up, he announced, ‘I’m in the zone, baby!’ “

Pratt, who did not show up at the post-red carpet events, also spent time with celebrity blogger Perez Hilton, who sources say hung out in Pratt’s hotel room and convinced Pratt to dress in disguise as an old man to avoid being further harassed by security on the premises.

Pratt put on a gray and white beard, stuffed a pillow under his shirt and hunched over to complete the costume, before crossing the street from the Hills red carpet to where the Inception movie premiere was taking place. “He greeted fans and took photos with who were waiting outside of the premiere,” an eyewitness says. “He told hassling security that he knew the laws, and that what he was doing was legal and there was nothing they could do.”

At one point he boarded a double-decker bus that was stopped on Hollywood Boulevard and shouted from the top. “He even offered to pay the driver if he could take it over for the night but the driver politely declined,” an observer says.

In between various Tweets and Twitpics to Hilton, Hills star Brody Jenner and The City‘s Roxy Olin, Pratt stopped at Twenty Five Degrees, a restaurant at the hotel. “He offered to buy the entire restaurant a drink, but the general manager said no,” an employee at the eatery tells PEOPLE. “The manager didn’t want things getting too crazy.”

Another employee at the diner said Spencer was courteous. “He was very sweet and very polite,” the observer said. “He didn’t seem like a bad guy at all. And he was a good tipper!” –Dahvi Shira

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