"Teen Mom" star Ryan Edwards really killed the mood -- one day after he and his wife announced they're expecting their first child, he went and got his ass arrested.
Law enforcement sources tell us ... the 30-year-old was busted Tuesday at his house in Tennessee when cops executed a warrant for violating probation. We're told he posted bail Wednesday morning. He's already on probation for a previous heroin case.
Ryan reportedly had a $10k-a-week heroin addiction before going to rehab -- and MTV cameras captured him slurring his speech and falling asleep at the wheel on his way to his wedding last year.
The arrest comes on the heels of his 21-year-old wife, Mackenzie Standifer, revealing she's pregnant. It will be his second kid -- he and fellow "Teen Mom" star Maci Bookout have a 9-year-old son.