If it was something very simple and I felt like my trivial suggestion would be enough to help them out, I'd give them that. Using your example, I simply would've suggested the caps lock key and been done with it. Granted, at that point, they may tell me to go lay my sick arse back in bed because they didn't know I'm an IT guy, but that'd be their loss.

But no way am I sitting down and debugging or troubleshooting their issue, I'm not being paid! lol.

It's funny though, because I find myself in this same position more often than I'd think I would. I find myself having to hold my tongue so I don't get distracted from my own daily errands on my days off. Plus, no one likes a know-it-all, right?