Ronnie Ortiz-Magro and Jen Harley Book it to Disney World in a Bad Mood

Ronnie Ortiz-Magro and Jen Harley look like future legal trouble walking -- even when they're heading for Disney World.

The on and off couple were not looking in the mood for travel, or anything else, as they boarded a flight from Las Vegas to Orlando. To be fair, they were flying Spirit at 2:45 AM ... so that could explain their faces. Other travelers tell us Jen seemed irritated and barked at Ronnie.

We'd chalk that up to the early hour, but then again ... these 2 have a serious history.

Once on board, we're told Ronnie sat 3 rows behind Jen and their 1-year-old daughter, Ariana Sky. They didn't speak AT ALL on the flight. We don't know if they intentionally sat apart, or if they weren't able to book next to each other -- it was a pretty full flight.

When they landed, we're told Jen yelled at Ron to grab their bags, which he did without any argument ... before they hopped into a black SUV.

A source close to the couple tells TMZ ... Ronnie is NOT filming anything there for "Jersey Shore." We're told the plan was for him and his family to celebrate Father's Day at Disney World.

The trip comes nearly a month after Jen was arrested for a New Year's Eve incident when she allegedly threw an ashtray at the reality star.

As we first reported ... Harley was arrested in Vegas on May 16 after she called cops to report someone with a gun. When cops arrived, she was the one hauled off after cops discovered she had an outstanding warrant.

Surveillance video showed Ronnie walking out of a club on the night in question ... with what appeared to be a bloody face. The fight apparently didn't end there cause when Jen got home that night, she allegedly found her home ransacked. She accused Ronnie of breaking a flat-screen TV among other things.