when Jeff's fighting in the warehouse, he beats up about six people. One of them has a red bandanna on, which gets knocked off. In the next frame, the bandanna is back on the guy's head.
When the gas tank explodes behind the burning Tanaka, a cut-away to a fake Tanaka body and a differently-burning tank is noticeable, mere frames before.
The Korean mafia bosses are called "Oyabun", which is a Japanese term for mafia boss.
When "Jeff" is fighting the gang of thugs in the antique store at the beginning, he knocks the guy through the window (same one he pulled through at the start of the fight). When the guy is shown landing, there is a glimpse of a blue landing mat just outside the window.
When Jeff and Adam are chasing Tanaka, Tanaka hits a truck with his car. Another car falls on his. In the car that is on top, the crew is reflected in the front window.
When Tanaka is being transported in a police car, he hits the driver, causing the car to lose control and flip. The gas canister used to flip the car is visible on the road as the car flips.