What a birdbrain!

The vandal accused of hijacking a cherry picker last month to scrawl “Bird God” on Brooklyn’s Grand Army Plaza arch struck again Thursday — this time using a ladder and a Sharpie to scrawl a bizarre avian-themed rant on the historic arch’s walls, police said.

Denis Shelagin, 36, of Washington state was busted at 6:30 a.m. for the latest stunt in which he allegedly scribbled, “If you cripple or kill any more of my birds then I will innihilate [sic] you in this next CARTEL WAR.”

The jibber-jabber continued, “We birds are the real Mafia. You keep messing with us anduwill [sic] mess with a nazi [sic] style human torture extreme.”

Shelagin was hit with a desk appearance ticket and released.

But passersby said their feathers were ruffled by the inexplicable vandalism.

“Believe me, I love birds, too, but this is just completely mental,” said Ewnetu Zegeya, 64, from Bedford-Stuyvesant.

“Something has to be done because this is a historic landmark in Brooklyn. It’s sad to see.”

Timothy Sedora, a professor at Bronx Community College, added, “The writing doesn’t make any sense to me . . . hopefully it’s not a real threat.”

The Sharpie graffiti also proclaims: “No bird — God’s grace will be great upon your soul on the judgement day” and “This is when you begin to live the lives.”

Shelagin’s first flap on Dec. 29 ended in his arrest.

He allegedly swiped a cherry picker meant for a holiday menorah lighting and wrote “Bird God” in giant block letters about 40 feet off of the ground.

Too bad for the bird lover he couldn’t fly — Shelagin couldn’t figure out how to get the lift back down and had to be helped down by the NYPD’s Emergency Service Unit.

He was promptly arrested and charged with making graffiti, criminal mischief and grand larceny.

Shelagin told cops at the time that his great-great-grandfather had ordered him — in a letter penned in 1960 — to use the crane to deface the arch, according to a criminal complaint.

He also claimed that he was worried something would happen to him if he didn’t follow through, the court papers state.

Shelagin was ultimately released on his own recognizance.

A Parks Department spokeswoman said removing the graffiti after the Dec. 29 incident likely cost the city $5,000 and took roughly two days.

Officials didn’t know how much repairing the latest vandalism would cost.

Shelagin is due back in court for the Dec. 29 incident on March 2.

Additional reporting by Rich Calder