Goodnight
I always assume that 'goodnight' should be the warmest greeting of all time, especially when it is from someone you fairly fond of. It is amazing when they say 'sleep tight' or 'sweet dream', even though none of us know what does 'sleep well' exactly means. Till we are all grown-ups, expressions are being swallowed and we started to mumbling to ourselves.
You mumbled 'goodnight', looking forward to receive a reply from the other side of conversation, yet you reach no avail.