Prepare yourself for one butt-kickin’ workout in this Southie warehouse that’s home to the kind of bare-bones boxing that would make Rocky Balboa proud. It’s old-school, with real rings and veteran fighters leading classes for proper jabs and evasive techniques. The punchline: There’s zero intimidation. Competitive fighters train alongside novices and kids, all with strength, speed, stamina, balance and agility goals. Stay tuned for the 23 Hour Toolbox to stay on track outside the ring.