So we are talking about friendliness (metta) thus meta-friendliness (see what i did there?).
A common saying amongst those that practice seems to be “Sabbe sattā sukhi hontu” meant as “May all beings be well (or happy)”. And usually translated as:
Sabbe = all
Sattā = beings
Sukhi = happy
Hontu = may they be
I think I rather prefer the “Sabbe satta bhavantu sukhitatta!” meant as “May all beings become thus happy!” but let’s pick this apart a bit with the help of contextual reference in pali scripts:
Sabbe = all (without exception)
Sattā = living beings (also hanging, clinging, attached – describes the conditioned state)
Bhavantu = become (mental development)
Sukhi = happy , with joy, at ease (released)
Tatta = thence, thereupon, future, afterwards
So really we are wishing release, ease to all non-attainers of the highest state and wishing that they develop to that state (or get some release, fruit from the path). This is for those born or yet to be born as those yet to be born are still conditioned. Knowing that the 8-fold path is the way to true happiness this also hints at becoming at ease through “that which must be done” i.e. mental development. This once again proves that these oft-used phrases are rather more nuanced than initially seen.
As metta practice is one of the Brahma vihara (divine dwellings) it is well to do this for the benefit of others and also for dealing with the defilements such as hate, greed etc. As a side note, it is often recommended that those who are obsessed with sensual pleasure actually use asubha (disgust) meditation as an object instead.
In actual practice, it is often difficult at times to settle directing metta at even some of our closest beings as particularly when they have frustrated and annoyed us. One great way of dealing with this is spending some time thinking about the good things/times from/with that being; this allows the metta to literally shine through.
With metta 😉