A soiree, or party, to which one was not invited, especially when in close range. From sui, by oneself (as in suicide) and soiree, from being near a loud party yet being alone. Pronunciation mutated to form suisare.
'Love Thy Neighbor' seemed an outdated notion, a souvenir of a vanished world, everyone now sheltering indoors, regarding their neighbors as a threat, overtaken by suisociophobia.