Patrick Schwarzenegger Involved in Los Angeles Car Chase ... Cops Investigate

2/17/2015 12:40 AM PST

Patrick Schwarzenegger -- Involved in L.A. Car Chase ... Cops Launch Investigation


Patrick Schwarzenegger got himself in one of those famous L.A. car chases -- but this one started with a simple splash of water ... and ended with a 2-car collision. 

Law enforcement sources tell TMZ ... Patrick was driving in the San Fernando Valley last week when some guy drove up on him and threw a bottle full of water on Patrick's whip and then bolted.   

We're told Patrick got pissed and started chasing the guy, who at some point banged a u-turn and ended up ramming Patrick's car.  Although the damage was minor ... the guy fled the scene. 

Patrick drove on to hook-up with GF Miley Cyrus for lunch at a nearby restaurant and called cops from there. Officers showed up, took a report ... and opened an assault with a deadly weapon investigation.

Bonus for cops -- they got to meet Miley, who we're told was wearing a sheer top with star pasties underneath.