Simple way to centralize message showing. Now we can inject MessageShower into whatever we want. In BaseActivity class I'm forwarding all CanShowMessage interfece's methods to MessageShower.

ActivityModule.java

//Provide different MessageShowers for different qualifiers

    @PerActivity
    @Provides
    MessageShower provideMessageShower(@ActivityContext Context context,
                                       PreferencesManager preferencesManager) {
        return new ToastMessageShower(context, preferencesManager);
    }

    @Named("login")
    @PerActivity
    @Provides
    MessageShower provideLoginMessageShower(@ActivityContext Context context) {
        return new LoginToastMessageShower(context);
    }

BaseActivity.java

//There is no really big profit to use TBinding generic here
public abstract class BaseActivity<TBinding extends ViewDataBinding, TPresenter extends BasePresenter>
        extends BaseCalligraphyActivity
        implements HasActivityComponent, CanShowMessage {
    @Inject
    protected MessageShower messageShower;
    private TBinding binding;
    private ActivityComponent activityComponent;
    private CompositeSubscription compositeSubscription;

    @Override
    public ActivityComponent getActivityComponent() {
        return activityComponent;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        buildActivityComponent();

        super.onCreate(savedInstanceState);

        binding = inflateBinding();

        if (getPresenter() != null) {
            getPresenter().onCreate();
        }
    }

    private void buildActivityComponent() {
        activityComponent = DaggerActivityComponent.builder()
                .appComponent(getAppComponent())
                .activityModule(new ActivityModule(this))
                .build();

        inject(activityComponent);
    }

    protected abstract TBinding inflateBinding();

    @Nullable
    public abstract TPresenter getPresenter();

    protected AppComponent getAppComponent() {
        return ManagerApplication.getApplication().getAppComponent();
    }

    protected abstract void inject(ActivityComponent activityComponent);

    final protected void addSubscription(Subscription subscription) {
        if (compositeSubscription == null || compositeSubscription.isUnsubscribed()) {
            compositeSubscription = new CompositeSubscription();
        }
        compositeSubscription.add(subscription);
    }

    @Override
    protected void onStart() {
        super.onStart();
        if (getPresenter() != null) {
            getPresenter().onStart();
        }
    }

    @Override
    protected void onStop() {
        if (getPresenter() != null) {
            getPresenter().onStop();
        }
        unsubscribeComposite();
        super.onStop();
    }

    private void unsubscribeComposite() {
        if (compositeSubscription != null && compositeSubscription.hasSubscriptions()) {
            compositeSubscription.unsubscribe();
            compositeSubscription = null;
        }
    }

    @Override
    protected void onDestroy() {
        if (getPresenter() != null) {
            getPresenter().onDestroy();
        }

        super.onDestroy();
    }

    @Nullable
    public TBinding getBinding() {
        return binding;
    }

    @Override
    public void showMessage(String message) {
        messageShower.showMessage(message);
    }

    @Override
    public void showMessage(@StringRes int messageRes) {
        messageShower.showMessage(messageRes);
    }

    @Override
    public void showMessage(Throwable throwable) {
        messageShower.showMessage(throwable);
    }
}

LoginToastMessageShower.java

public class LoginToastMessageShower implements MessageShower {
    @NonNull private final Context context;

    public LoginToastMessageShower(@NonNull Context context) {
        this.context = context;
    }

    @Override
    public void showMessage(@NonNull String message) {
        Toast.makeText(context, message, Toast.LENGTH_SHORT).show();
    }

    @Override
    public void showMessage(@StringRes int messageRes) {
        showMessage(context.getString(messageRes));
    }

    @Override
    public void showMessage(@NonNull Throwable throwable) {
        if (throwable instanceof RxRuntimeException) {
            throwable = throwable.getCause();
        }

        if (throwable instanceof HasLocalizedMessage) {
            showMessage(((HasLocalizedMessage) throwable).getMessage(context));
        } else {
            showMessage(throwable.getMessage());
        }

        Timber.e(throwable, "Showing error message in %s", context.getClass().getName());
    }
}

MessageShower.java

public interface MessageShower extends CanShowMessage {
}

ToastMessageShower.java

public class ToastMessageShower implements MessageShower {
    @NonNull private final Context context;
    @NonNull private final PreferencesManager preferencesManager;

    public ToastMessageShower(@NonNull Context context,@NonNull PreferencesManager preferencesManager) {
        this.context = context;
        this.preferencesManager = preferencesManager;
    }

    @Override
    public void showMessage(@NonNull String message) {
        Toast.makeText(context, message, Toast.LENGTH_SHORT).show();
    }

    @Override
    public void showMessage(@StringRes int messageRes) {
        showMessage(context.getString(messageRes));
    }

    @Override
    public void showMessage(@NonNull Throwable throwable) {
        if (throwable instanceof RxRuntimeException) {
            throwable = throwable.getCause();
        }

        if (throwable instanceof UnauthorizedException) {
            onUnauthorized();
        } else if (throwable instanceof HasLocalizedMessage) {
            showMessage(((HasLocalizedMessage) throwable).getMessage(context));
        } else {
            showMessage(throwable.getMessage());
        }

        Timber.e(throwable, "Showing error message in %s", context.getClass().getName());
    }

    private void onUnauthorized() {
        Toast.makeText(context, R.string.unauthorized_error_message, Toast.LENGTH_SHORT).show();
        preferencesManager.setToken("");
        LoginActivity.start(context);
    }
}