Is it a bad practice to use negative margins in Android?

Instead of negative margins you can use: translationX and translationY.

Example:

android:layout_marginBottom = -2dp

android:translationY = -2dp

UPDATE: Have in mind that the whole view is translated.

Hope this will help someone. Here is working sample code using ConstraintLayout based on @CommonsWare's answer:

Add an helper view (height 0dp, width constrained to parent) at the bottom of your base view, at the bottom add the margin you want. Then position your view below this one, effectively allowing it to have a "negative" margin but without having to use any unsupported negative value.

Sample code:

<TextView
    android:id="@+id/below"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="#F1B36D"
    android:padding="30dp"
    android:text="I'm below"
    android:textColor="#ffffff"
    android:textSize="48sp"
    android:textAlignment="center"
    tools:layout_editor_absoluteX="129dp"
    tools:layout_editor_absoluteY="0dp" />

<android.support.v4.widget.Space
    android:id="@+id/space"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:layout_marginBottom="32dp"
    app:layout_constraintBottom_toBottomOf="@+id/below"
    app:layout_constraintLeft_toLeftOf="@id/below"
    app:layout_constraintRight_toRightOf="@id/below" />

<TextView
    android:id="@+id/top"
    android:layout_width="100dp"
    android:layout_height="60dp"
    android:textAlignment="center"
    android:textColor="#ffffff"
    android:text="I'M ON TOP!"
    android:background="#676563"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/space" />

Output:

In 2010, @RomainGuy (core Android engineer) stated that negative margins had unspecified behavior.

In 2011, @RomainGuy stated that you can use negative margins on LinearLayout and RelativeLayout.

In 2016, @RomainGuy stated that they have never been officially supported and won't be supported by ConstraintLayout.

In December 2020(v2.1.0, official release June 2021), negative margin support for constraints has been added to ConstraintLayout.

It is easy to work around this limitation though.

Add a helper view (height 0dp, width constrained to parent) at the bottom of your base view, at the bottom add the margin you want.
Then position your view below this one, effectively allowing it to have a "negative" margin but without having to use any unsupported negative value.

In case you want use negative margin,set enough padding for container and its clipToPadding to false and set negative margin for it's children so it won't clip the child view!