If you want we can start a thread on “Earth’s Most Horrifying Organisms”. It’s a rather long list of nightmare fuel and I’m no expert by any means. 
Stumbled across some unfamiliar word use in this discussion and it reminded me of this thread.
rattletrap: an old or rickety vehicle
rattrap: a device for trapping rats; a dilapidated building (e.g., one inhabited by rats); a difficult or entangling situation; (adj., usually describing a mouth or jaw) thin-lipped, wide and tight, especially connoting a hostile or menacing expression
Also numbered stars such as 18 Scorpii, one of the closest Sunlike stars.
talon: claw
talion: retaliation, retribution
principle: a fundamental assumption
principal: primary, first level in importance
semiotic: relating to signs or symptoms
semetic: [probably not a real word? semet = anther]
semitic: of any of a number of peoples of ancient southwestern Asia and East Africa
Maybe cheating a bit because these are proper names, but
Pantheon: an ancient Roman temple in Rome
Parthenon: an ancient Greek temple in Athens
I used to get these confused all the time, because the name “Pantheon” is clearly from Greek roots (“pan” = all, “theion” = of a god), while Parthenon, although also Greek, has a less obvious root.
trial and trail
I remember that a path might have a rail fence.
I can still screw it up after a long day at work.
Martial arts and Marital
execrate: to denounce, curse
excrete: to discharge material
excoriate: to flay, strongly denounce
Discreet/discrete: distinctly diffident/distinctly different
Coruscating/excoriating: flashing and sparkling/flaying and disembowelling
In the realm of simple typing errors, I would sometimes type Louise as Lousie (oops), and I lost count of the times I missed out an unimportant word like “not”.
Not always that different…
I didn’t even know talion was an English word until I read your post today. I knew it as a French word with the same meaning, and that only because I read the novel Les Sept Jours du Talion by Patrick Senécal. It’s worth reading if you know French, but like a lot of his books, it’s not for the faint of heart.
Maybe the same if you scourged one of those sparkly vampires?
censor: (1) v., to suppress or prevent publication of a work, opinion, etc.; (2) n., one who censors
censure: (1) v., to formally rebuke; (2) n. a formal rebuke
censer: n., a kind of incense burner
sensor: a device, often electronic, that measures some physical phenomenon
senser: a person or animal that senses
Along those lines:
phosphorus: Chemical element, nonmetal, atomic number 15
Phosphorous: Containing, characteristic of, pertaining to, or resembling phosphorus
Colombia is in America, too. 
It drives me crazy when people claim they raised a family. We raise sheep and rear children. Secondly, if you are not concerned about a topic , you could NOT care less. Think about it. My son recently found out they were expecting a baby. I jokingly commented the “to heir is human!” He has a Masters degree and was valedictorian years ago but needed me to explain my play on words. Ugh! I teased him that if he were bilingual I could overlook errors but if he is only fluent in English, he should speak it well. Being articulate opens many doors. Loved this post. I personally struggle with effect and affect continuously.
To be fair, not everyone is familiar with Alexander Pope, and that isn’t a phrase in constant use among people of a younger persuasion, I’d guess
Besides, to forgive is divine…
Here’s an obscure one I just came across in a novel:
Demurred: raise objections/show reluctance
Deferred: [depending on context] withdrew/suppressed objections/ accepted someone else’s decision
continuous: absolutely uninterrupted
continual: recurring at frequent intervals
This isn’t really a word you can get confused’. It is an idiom, and we’ve had at least two threads dedicated to it.
Put me in the camp that says ‘you could care less’ is a perfectly cromulent idiom.
However, ‘cromulent’ is itself a word with debatable status.
This is not a joke that is obvious without seeing it in print, since he would have no way of knowing you were making a play on words that are pronounced identically. But go ahead and insult your son for not getting your random joke.