My worst time is not as bad as most of the ones I've read.
Went to SDCC in 2010. I had been in 2004, 2005, and 2007 and had previously worn different Obi-Wan costumes, a Stormtrooper and my Darth Vader.
Between 2007 and 2010 I had made many upgrades to my Vader costume. One of them was building some new inner shoe lifts to give me an extra inch in height. I had tried them on and walked around the house and they felt fine.
So for SDCC 2010 I only take my Vader costume. I was planning on wearing it on Friday and Saturday. I was hoping this would be a big deal for me, maybe see my photo all over the net and hopefully on a few news sites. I was really excited.
Friday morning I suit up and we leave the hotel (me, my brother, and my 10 year old daughter). I climb in the back of the van and my brother drives us over to the train station.
Because of where our hotel was, and all the stops the trolley makes, I'm standing in these jacked-up boots for about an hour before we even get to the convention center. Then I have to walk all the way up, my feet are already hurting and I'm starting to sweat because I'm getting nervous about my feet holding up.
Once inside I'm burning up, but my helmet has a fan so I put in on hoping it will cool me down. My brother went off do do his own thing and my daughter is my 'handler' for the day as well as my photographer.
All suited up I enter the convention floor and I can't see anything. I'm getting great reactions and taking lots of pictures but I'm burning up, covered in sweat, I can't see (helmet lenses covered in fog), and my feet are killing me. I can barely walk, but I get next to a display and stand for more photos.
All of a sudden I can't see my daughter and I have a mini-panic attack. Worried that something might have happened I call out to her and she's right next to me, I just couldn't see her. This makes me so overwhelmed that I can't stop sweating due to nerves.
I've only been in costume for about 45 minutes to an hour and I just can't take it anymore. My ankles feel like someone hit them full-force with a baseball bat, I can hardly put any weight on them. I take my helmet off, take my cod off, and we find a place for me to sit down. I though if I could just cool off and rest my feet for a minute I'd be fine.
After about 10 minutes of sitting I realize I'm not having any fun, and my daughter is being a real trooper sitting with me but we're both missing out on the best Con.
So, defeated, I take my boots off and we start heading back to the trolley to go back to the hotel. I felt like a total loser wearing half a Vader costume (no helmet, gloves, or boots) plus I'm now wearing only socks and without the boots I'm only 5'8".
So my grand expectations were ruined, it was not meant to be. And to make things worse, somewhere in all that I hit my helmet and broke one of the tusks off and broke the fiberglass.
I decided 'that was that' and after I changed in the hotel we went back and we had a BLAST Friday and Saturday. On Saturday we went to the Family Guy panel in the morning and the Mythbusters panel that night, both of which we could not have done had I been in costume all day. I ended up having a better time with my daughter without the costume, and I'm actually happy that I suffered an epic, horrible costume fail.
Costume is now fixed, I made new boot lifts and wore then for 4-5 hours last month at a local Con and my Vader costume in back in business.