Add this to your ~/.vimrc:
" Add reviewers as a dictionary
set dictionary=~/.reviewers
" Use dictionary in completion suggestions
set complete+=k
" Consider . as a keyword, makes sure user.name is completed in one go
set iskeyword+=.
Add your reviewers to ~/.reviewers. Each line contains one reviewer username.
Now when in vim, insert the first letters of a reviewers name, then complete the name using ctrl+n / ctrl+p.