a baleful look.
a black lie.
a dark purpose.
a sinister smile.
bar sinister.
black deeds.
dark undercurrents of ethnic hostility.
Darth Vader of the dark side.
forbidding thunderclouds.
his black heart has concocted yet another black deed.
his threatening behavior.
his tone became menacing.
ominous rumblings of discontent.
sinister storm clouds.
the scheme of some sinister intelligence bent on punishing him.
the situation became ugly.
ugly black clouds.