(informal) directly using one's own chopsticks to take food to one's own bowl instead of using the designated chopsticks, which is considered a breach of etiquette

difficult / hard, probably impossible

to use / to employ / to make use of, to apply / to spend

a chopstick

chopstick

use one thing for many purposes / work someone hard

to use one's head

direct, straight, frank

sincere, straightforward, proper, frank / simple, not extravagant, not expensive, less formal

to do one's duty, be on duty