What is the balking pattern, and where would you use it?

Balking is the "if you are already doing it, do nothing" pattern: check the state under the lock, and if the action is not appropriate right now, return at once rather than blocking.

void save() {
    synchronized (this) {
        if (!changed) {
            return;           // balk: nothing to do
        }
        changed = false;
    }
    writeToDisk();            // the slow part, outside the lock
}

Autosave, lazy refresh and idempotent start/stop methods are typical. Its opposite is guarded suspension, which waits for the state instead of giving up. Choosing between them is choosing whether a caller would rather be delayed or told no.