Inspired by similar magic tricks to make 2+2=5 through messing with IntegerCache, I present two more devious tricks to make booleans behave in unexpected ways.

BooleanMagic.java

import sun.misc.Unsafe;
import java.lang.reflect.Field;

public class BooleanMagic {
    private static void doImpossibleBool() {
        boolean impossible = ImpossibleBool.IMPOSSIBLE_BOOL;

        if (impossible == true) {
            System.out.println("Value was true");
        } else if (impossible == false) {
            System.out.println("Value was false");
        } else if (impossible == impossible) {
            System.out.println("Value was impossible");
        }
    }

    private static void doOppositeDay() {
        makeOppositeDay();

        Boolean alwaysTrue = true;
        if (alwaysTrue) {
            System.out.println("The world is normal");
        } else {
            System.out.println("Today is opposite day");
        }

        System.out.println("True = " + Boolean.valueOf(true));
        System.out.println("False = " + Boolean.valueOf(false));
    }

    public static void main(String[] args) throws Exception {
        doImpossibleBool();
        System.out.println();
        doOppositeDay();
    }

    private static void makeOppositeDay() {
        try {
            Field theUnsafe = Class.forName("sun.misc.Unsafe").getDeclaredField("theUnsafe");
            theUnsafe.setAccessible(true);
            Unsafe unsafe = (Unsafe) theUnsafe.get(null);

            // Overwrite the raw value of "true" to false
            unsafe.putByte(Boolean.TRUE, unsafe.objectFieldOffset(Boolean.class.getDeclaredField("value")), (byte) 0);

            // Overwrite the raw value of "false" to true
            unsafe.putByte(Boolean.FALSE, unsafe.objectFieldOffset(Boolean.class.getDeclaredField("value")), (byte) 1);
        } catch (Exception ignore) {}
    }

    private static class ImpossibleBool {
        // This cannot be final or passed in a method otherwise it'll become a compile-time constant or lose its modified value
        public static boolean IMPOSSIBLE_BOOL = true;

        static {
            try {
                Field theUnsafe = Class.forName("sun.misc.Unsafe").getDeclaredField("theUnsafe");
                theUnsafe.setAccessible(true);
                Unsafe unsafe = (Unsafe) theUnsafe.get(null);
                
                // Setting a boolean value to 2 makes any direct comparisons against other booleans (0 or 1) always false
                // Regular conditonal checks like if (IMPOSSIBLE_BOOL) will behave as if the value is true
                unsafe.putInt(ImpossibleBool.class, unsafe.staticFieldOffset(ImpossibleBool.class.getDeclaredField("IMPOSSIBLE_BOOL")), 2);
            } catch (Exception ignore) {}
        }
    }
}