Or, in a less macabre example, his poke is strong enough to either send his foe flying into orbit, or sent flying around the world right back to where Bob is.
Downplayed: The finger poke is only used sporadically, and only for comic effect against a nuisance of a foe.
Bob spent decades training to be that powerful, or got this power from a magical source.
Alternatively, Bob is from another planet with much, much stronger gravity, and his strength is proportionate to the gravity of the planet, giving the impression of him being far stronger than he really is on a world with much lighter gravity.
He hits someone in a pressure point. In real life, getting hit there hard enough can kill you.
Inverted: Bob tries this at first and it dosen't work...so he decides to train to get stronger, so then he can pull it off successfully.
The finger poke ends up harming Bob more than the foe its used against.
Defied: "I'd love to use my move to send this guy flying, but what if this guy ended up falling onto someone? Better hold back..."
Discussed: "Remember the look on that guys face when i flicked him right across the room?"
Conversed: "You see, strong characters do this to establish not only how strong they are, but also show how awesome them are."
Implied: Is hinted that an otherwise meek character has done this off-screen to a foe.
Bob's finger poke is liable to cause collateral damage to people and buildings nearby, and he has no Hero Insurance to fall back on.
Alternatively, the finger poke is a representation that if Bob's finger poke alone is that powerful, then if Bob unleashed his full power, it would be catastrophic.
Bob's finger poke may accidentally kill his foe, either because Bob didn't know his own strength, or the mook was much weaker than he looked.
The villain Bob does the finger poke on happens to be a weak mook, and the poke would have no effect on a much stronger foe.
Also, what other people percieve as Bob having incredible power in such a move alone is seen as a trivial, weak move among Bob's own kind.
Bob has to be very careful with the finger poke, as he has little to no control over his strength, and could easily hurt someone by accident due to it.
But, Bob knows to only do the finger poke in remote areas when no one outside of his foe is around to be harmed indirectly by it.
Alternatively, he learns to only use it as a last resort.
Played For Laughs:
Bob does this frequently to all of the people he hates or have tormented him.
A several foot tall, testosterone poisoned, insurmountable muscleman is reduced to a fetal positioned crybaby just by Bob poking him in the stomach.
Played For Drama:
The finger poke drives Bob into an existential crisis, that having so much power could make him dangerous to be around those who he loves.
Alternatively, the poke can be used to start off a tense fight scene or conclude a Let's Get Dangerous moment.
Untwisted: Bob seemingly fails at doing the finger poke and breaks his arm out doing it...but then it turns out his real power can only be unlocked by extreme pain, allowing him to deliver the real deal.
Necessary Weasel: The finger poke has to be done to establish to newcomers that this guy is supposed to be a very powerful character.
Intended Audience Reaction: The film presents Bob as an otherwise unremarkable person, prior to meeting his seemingly stronger foe, who he shockingly takes down with an effortless jab at a pressure point.