Okay, let's talk public transportation. Germs and contamination are an enormous part of my OCD, and public transportation seems to me to be a breeding ground for bacterial nastiness.
One of the hardest things I've ever done, OCD-wise, was taking a class at my local community college and having to take the bus to and from school twice a week. I called it the 'Torture Chamber on Wheels.' Not the catchiest nickname in the world perhaps, but it accurately described my feelings about the dreaded bus. I hated every millisecond of those bi-weekly trips.
I always used my coat sleeve to grab onto the bars, and inwardly cursed the bus driver whenever he started the bus up again before I had gotten into my seat, causing me to lose my balance and find myself grabbing onto something to steady myself . . . without having time to pull my sleeve over my hand. Gross!
If possible, I would find a set of empty seats, sit in the aisle seat, and place my backpack on the window seat. There was a double discouragement that way to anyone who might consider sitting next to me. My backpack made the seat next to me look semi-reserved-ish, and the fact that I was in the aisle seat would make it so that anyone wanting to sit next to me would have to scoot past my legs (most unpleasant on the one or two occasions it happened, but it was rare enough that the potential risk was outweighed by the benefits of sitting alone). This strategy usually worked on the first leg of the bus ride. On the second leg it was impossible to get a seat by myself. I just had to locate the cleanest looking individual with an empty seat next to them.
The smell, the warmth, the people, and the general dirtiness were unbearable. I had to take a shower and throw my clothes in the washer as soon as I got off the bus, and I always took my shoes off before I came inside. I wore the same shoes on the bus every time, and at the end of the term I threw them away.
Everything I took on the bus was thereafter contaminated. My notebook and textbook were things I couldn't bring myself to touch at home. I read my assignments and notes on the bus, and I must have written my papers from my memories of the lectures and text, since I can't imagine referring to them at home. My backpack was a thing of indescribable filthiness that had to be put in one precise place so that the contamination was somewhat contained. I remember one time a member of my family set my backpack on a chair for some reason. I begged them to take it off, with such panicky insistence that I was very nearly yelling. Alarmed, they took it off immediately, but even so I almost burst into tears on the spot, and I wouldn't sit in that chair for weeks.
I survived that term somehow, but I think that's a prime example of making sure you don't bite off more than you can chew when tackling your OCD. It's been a few years since I took that class. Since then I have discovered the miracle of online classes, and I've only been on a bus once since that time, when I had no other choice. Most people would probably laugh if I called my bus experience traumatizing, but it was for me. The other day as I was walking with my family through the bus station to get to another destination, all my feelings of revulsion resurfaced. It was outdoors, nobody was near me, and I knew I didn't have to get on the bus, but I couldn't wait to get out of there.
I guess the point is: If you're going to tackle your OCD, yeah, you have to make yourself do hard things, but take it easy. As the old saying goes, if you set out to eat an elephant (which I always found kind of disgusting), do it one bite at a time. Don't try to swallow the elephant whole. As I can testify, you're more likely to choke yourself than get rid of the elephant, and you won't want to try it again.