Numeric values in the everyday world are "positive" or "negative" only in relation to some artificially assigned zero point. If we use the surrounding seabed as a zero point, the height of an undersea mountain is expressed as a positive value. But if we use sea level as the zero point, then its height is a negative value.

So, all we need to do to create negative posts is to randomly assign the value of "zero" to some post besides the original one. Like this one! That would make the "first" post to this thread number -23.