I've had three that make me wince every time I think about them:
1) I was in Carlisle, listening to music and looking at my phone and I was heading to GAME the shop. I had a rough idea of where it was, and out the top of my eye I could see the purple of the storefront. However, right next door there was also an Ann Summers shop, with a similar coloured storefront. It wasn't until I walked in, realised there was a step where there hadn't been one before and looked up to see about thirty women from the ages of about 30 down to 15 staring at me. Time. ****ing. Stopped. I wasn't sure if I should tell them I'd walked into the wrong shop, because they'd all think I was in there being a perv or retarded for not getting the right shop or something. All the time I was thinking this, seconds ticked on, and everyone kept staring at me and eventually I backed out into a group of 19 year old girls... It wasn't a good day.
2) Mountain biking on the fell and there was this huge, (like 200 hundred odd), crowd of people all sitting along the sides of this mountain biking path. I went through the first lot without much bother, but they were all watching me and I hate that sort of look people give you. Anyway, got to a jump, did it well but landed and my wheel washed out. The laughs, the s******* and finally the "Are you OK?" I tried to make a joke of it and that failed worse then the jump...
3) Back in Carlisle, when I was younger I loved jumping those bollard things. I had really baggy jeans on, caught the bottom on the bollard and full on faceplanted the ground right in the town centre. Broke my nose, got laughed at by other people and nothing hurt as much as my pride.
Those would be my three, the first being by far the most embarrassing... Was so tempted to make it sound like I was buying something for a girlfriend I didn't have at the time... But no, I froze and when I did move it was straight into a group of attractive, female women who were my own age.