Man Claiming to Be Nia Long's Son Arrested for Assault with Tent Pole

Being Nia Long's son is NOT a get-out-of-jail-free card, especially when you're NOT really her son at all -- as a guy found out after he allegedly smacked a stranger with a tent pole.

Law enforcement tells TMZ ... Tamir Rasool Morris was arrested last weekend in Santa Monica where cops say he assaulted a random person in a park. When officers questioned him, Morris told them his name was Massai Dorsey II ... which is the name of Nia's actual 23-year-old son.

What's creepy for Nia and her fam is this guy's clearly done some research ... because he also gave officers Massai's correct birth day and month, but finally slipped up with the year. We're told he was off by 2 years.

Of course, his web of lies fell apart when he was booked and fingerprinted ... which revealed his real name.

According to our sources, cops suspect Morris pulled Massai's info from social media, but Santa Monica PD wants to make it clear ... the real Massai was not at all involved in the incident, and his name was given without his knowledge.