little, slight, small
simple
The answer was a simple shrug.

careless, indifferent
casual, nonchalant
dismissive
half-hearted, helpless, resigned
weary
apologetic
self-deprecating
mental
With a mental shrug, he decided to tell the truth.

Gallic (BrE)

give
The boy gave a slight shrug and walked away.

in a shrug
She lifted her shoulders in a little shrug

with a shrug
‘I don't know!’ she said with a shrug.

shrug of
a shrug of resignation

a shrug of the/your shoulders
He replied with a shrug of his shoulders.

lightly, slightly
carelessly, dismissively, indifferently, nonchalantly, offhandedly
She shrugged nonchalantly and turned away.

casually
wearily
uncomfortably
apologetically, awkwardly, sheepishly
helplessly
He shrugged helplessly and said nothing.

innocently, modestly
good-naturedly
just, merely, only, simply
He merely shrugged his shoulders in reply.

Shrug is used with these nouns as the subject:
shoulder

Shrug is used with these nouns as the object:
shoulder