There's a definition of kusala here:
kusala: characterizes all which has pleasant and happy results: advantageous, meritorious, skilful, virtuous, morally good, good, right, prosperous, salutary, skilful. Especially used in its moral sense.
The Commentary defines the term as having three meanings:
- (psychologically, spiritually) healthy
- productive of pleasant and favourable results.
Kusala can also be defined as what arises on the basis of the three kusala·mūlas. In terms of action, ten main kusala actions are listed and called together kusala·kamma·pathas.
I think 'impulsive' isn't exactly the same as akusala.
Let's look at an antonym of 'impulsive', for example "cautious". Or @slova's answer suggests "slow" and "prudent". I imagine that someone who is not impulsive might think twice before speaking, look both ways before crossing the street, save their money instead of spending it ... but that (e.g. hoarding their money) is not necessarily kusala.
Or let's consider for example Siddhārtha Gautama's deciding to leave home: that story might (or might not) seem a bit "impulsive", but we shouldn't call it akusala.
Being impulsive might be one example of akusala (e.g. losing your temper and suddenly killing someone in anger), but there are other forms of akusala which are not impulsive (e.g. carefully planning a crime for a long time before doing it).
Also I hope that there are some forms of being impulsive that are not very akusala (for example impulsively deciding to try to help someone else, being impulsively kind).
You said that your "leader was talking about people who cannot control their cravings and wants, who are easily subjected to actions based on their whims and wants of their anger".
Things like cravings and anger (and ignorance) are known akusala-mūla which are translated/called/known in English the "three poisons" or "three unwholesome roots", also "three roots of evil" and "the three unwholesome mental states". In that phrase, akusala is translated as "unwholesome" or even evil.
As @sova mentioned in a comment it's the mental state (e.g. of anger) that's unwholesome, or the result (like the tree which grows from the "root") that's unwholesome.