Haha I love these random moments with people. I always join in on events whenever I see someone doing them, even though I know the loot is probably gonna be crap for me. Early on, there were people who would blitz in and help me out with a tough event, and now I am the one blitzing in and helping others.
I do wish there was a "You're welcome" emote though. The closest we have is Cheers, but that just makes your character say "Impressive", which really isn't a cheer at all.