Where "Grub" Comes From
The insect larva turned into a put-down. Green's Dictionary of Slang records this sense of a contemptible or unpleasant person, with an earliest Australian citation from 1968 (an American citation from 1967–68 is slightly earlier). It is common in Australian speech, including in commentary on dirty play in sport.
Sources: grub, n.1 (Green's Dictionary of Slang) · grub (Wiktionary)
“Whoever dented my car and drove off without leaving a note is a grub.”
“That was a grub of a tackle, and he knew it.”
"What kind of grub keys someone's car?"
How Aussies Actually Use It
A step down from "dropkick" or "ratbag" in severity — implies genuine contempt rather than affectionate ribbing.
Grub as an insult is blunt and meant to hurt. Unlike 'drop-kick', which can be used fondly about a mate who did something silly, calling someone a grub says you think they're low or dishonest, with no laughing along. It's what you'd say about someone who did something mean, sleazy or underhanded, so it tends to come out with real feeling behind it.
It's usually applied to a specific act ('that was a grub move') or a specific person after the fact, more than as a general nickname. You'll hear it in sport commentary and in everyday complaints about bad behaviour. It isn't a strong swear word, but it's not for the workplace or for polite company. Learner tip: don't confuse it with the ordinary noun for food (as in 'good grub') or the insect larva. The insult is a separate use of the word.
See also: Drop-Kick (milder, often affectionate put-down), Ratbag (another disapproving label), Dodgy (dishonest or unreliable).
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