Diki, I would've thought that Gary's (possible) leaving would've given you pause for thought enough to leave this alone for now.
I also think what Nigel just posted was a point well said.

If I was drinking Coffee at the time I read:
"Sure, I can be a bit sarcastic from time to time."
I assure you it would've been spurted all over my Computer Monitor in laughter.

Passive aggressiveness, be it in tone, words, or deeds, still comes from the same place as overt aggressiveness, it just manifests itself differently. A friendship, or Marriage, or ANY relationship (be it two people, or a group of people, e.g. a family) can still be poisoned just as surely by a consistent and persistent attitude or tone, as well as by a malicious or deadly physical act - and often it is more torturous in it's own way - as it usually takes much longer.