Scott Disick may have checked in to a posh rehab facility in Costa Rica earlier this month, but it was reported that the reality star checked out after just one day -- and he's already back in a big way!

After making an appearance at a club in Las Vegas last Monday, Disick lunched with several pals at the Montage in Beverly Hills on Friday afternoon, looking as cool as a cucumber. One of his male friends was holding a kid, so it could have been a mellow dads' day out, but given Scott's history, we think it's only a matter of time before he's back on the party circuit!

Even before he checked in to rehab, there were reports that Scott and baby mama Kourtney Kardashian were headed for Splitsville, and since he's been back, we haven't seen the two together at all. The separation rumors could be a plot line for Keeping Up With The Kardashians ... but with these two you never know!

"Even though they’re not married, this could be one of the messiest and most expensive splits ever," a source told Life & Style magazine earlier this week, adding that it could cost somewhere around $50 million. "[Scott] never uses his own cash," the source continued. "Even when he buys his kids expensive things, he charges it on credit cards that Kourtney pays for." Yikes!