if they say I never loved you / you know they are a liar

I'm quite petty, and I love convincing people who think intelligence is important that I'm smarter than they are.  From this, you might assume that I would be a big grammar nazi, perpetrating systematic, IBM-assisted genocide on unclean participles.  I find I can derive more immediate pleasure and greater satisfaction, however, from using my love of intellectually dominating towards rocking the pillars of faith that buttress grammar snobs' shaky feelings of superiority.  This is easy.  Here's your guide. 

Step 1:
Wait for the grammar snob to overhear something that compels him or her to make a meaningless correction.  You won't be waiting long.  They're on hair triggers. 

Step 2:
"Actually"
Beginning with this lets people know that they have been laboring under a misapprehension.  Keep your voice conversational, as though you were telling them an interesting thing you heard about naked mole rats rather than bringing them up short for doing something annoying. 

Strep 3:
Just say that the point they're correcting is perfectly acceptable English, "attested" (I enjoy using this word, as it suggests data) since Shakespeare.  This is almost always true; Shakespeare was quite free and loose with his words, famously.  If the person is more concerned about being correct in the future than being correct in this instance, this will often defuse them.  You'll have to repeat this tactic every time it comes up, though. 

Step 4:
If the amateur grammarian refuses to accept your authority on this matter simply because you can speak in an authoritative tone, escalate your rhetoric while retaining the same flat, disinterested air.  You know, because you are exceptionally well-read on matters of linguistics, that languages exist in a state of flux, and efforts to preserve them in a fixed state are not merely doomed, but laughably wrongheaded.  Ask them if they understood the sentence in which the grammatical "error" occured, and what the problem is if it communicated clearly to them. 

Step 5:
If your interlocutor still won't relent--and they probably won't, as by this point they have invested quite a bit of their self-worth into the conversation--use shame.  It is pretty trivial to construct an argument concerning class, race, the prestige of different regional speech patterns, access to education, and shibboleths, and so I leave it as an excercise to the reader.  Let them know that by correcting others, they are not educating them, but merely perpetuating an injustice based on the circumstances of their birth and early childhood.  Wither them.  If they are liberal, this should plunge them into a vertiginous shame spiral.  If they are conservative, they are a terrible person.

Step 6:
Repeat as desired, or until you no longer have friends who will talk to you about words.