Just realised that "Awoo!" is an excellent substitute for "Hello Fediverse!" That's ELEVEN characters saved. Think what you could say with eleven characters.
With 11 characters I can almost write my username.
11 characters is just enough for a your mum joke:
...
"So's yr mum"
You could also complement someone enthusiastically:
"Nice face!!"
--Thanks @cassolotl@cybre.space
Please respond with your own elegant uses of 11 characters!