Not exactly in WoW, but losing all my Vanilla screenshots and guild progression movies due to system reinstall. The earliest screenshots I have are already on BC pre-patch. :( I also regret losing contact with all but two WoW friends.
During Vanilla WoW I guess I don't regret much. Maybe going for T0, T1, T2 sets as a mage while these were not the greatest for min-maxing. I loved the look of those sets though. People were also kind of impressed on our first MC to see me wear complete Magister's Regalia.
I wish I would have played more when I enjoyed the game, you never really realize that some moments are the greatest, until after they're gone.
I started playing wow the first week it released. Made a night elf druid. Game was insanely awesome, completely blowing me away immediately.
Could not figure out how to get off of Teldrassil.
Eventually stop playing completely. Only start playing again near the middle of vanilla, hitting level cap shortly before TBC released.
Regret
Not pushing Arena or RBGs harder.
I was 110% in on Vanilla and got just about everything accomplished that a Priest could want during that time frame.
I do regret giving my 2nd (Rank 11) account away from Vanilla though. I dont have any of that awesomeness on live right now.
Is your character named after the rock or the movie?
I regret getting into the game in the first place because it consumed the past 7 years of my life. I also regret not getting into it sooner because I missed my opportunity to get Ashbringer and experience awesome stuff like the Corrupted Blood incident.
I regret switching my main. In Mists I switched to Pandaren Monk and in Legion I switched to Demon Hunter. I feel bad for not staying on my main until now. My Shaman has so many cool things and legacy items and now Im sad that all the stuff from later expansions are scattered across many different characters.
Besides that, maybe not being more engaging with my guildmates from my home town - I was so lucky to find people i clicked with. Not in contact with any of them anymore except one.
Not grazing enough when I was a young buck - I wasn't getting the carbs I needed so I became a Beta.
I'd want to say that I regret not having been in a good guild in Vanilla but I honestly think I was too new to MMO's to handle the climate. I was too used to the sporadic nature of Diablo.
SO I will go with wasting TBC with my ex PVPing. She hated doing any prep work for raiding that I really wanted to do so we just PvP'd most of the expansion. Badly at that. I still had some great times and a lot of fun thankfully but I really missed the boat on Black Temple, etc.
I regret not playing sooner, I was playing Lineage 2 back then in vanilla times and only tried WoW when TBC came out. I was pretty fun Lineage 2 with friends but I wish I tried vanilla back then. Now I can do it!
For trying to level, until around 35, as a FIRE mage. Man was it easier when i switched to frost.
I dont have any regrets in vanilla WoW.
I never finished naxx, but that whole situation was out of my control (server drama). basically I was in the top guild. the other faction wouldn't open the aq gates while we are progressing naxx, <insert drama>, guild implodes.
an unfortunate situation but its water off my back. I can't say I care very much about pve achievements. pretty typical pvp player attitude I guess.
my regrets are more along the lines of not quitting soon enough, installing WoD, things like that.
That i did not pushed my PvP Rank more.
I helped a lot of people in my guild with low level Dungeons or farming the T0 sets because i thought that the PvP system will be around forever. Then TBC came and all pvp was forced into Arenas