Word for silent expression of tickled shock at someone else's outburst
The word "bemused" may fit this context well.
As per Merriam Webster dictionary, the definition of this word is - to cause to have feelings of wry or tolerant amusement
A word I learned here at EL&U is...
gobsmacked
so shocked you cannot speak
coming from the slang word "gob" for "mouth"
It is informal, but a great word.