My worst one was going up this fairly steep hill. At the time, I didn't realise that there was a problem with the spark plugs (?) for some of my gears.
On the level approach, the car was doing fine. I was on 4th gear going at 30mph. Soon as I started to climb, I noticed the car struggling, so I put it down to 3rd, and this was when it went even worse! It won't even go past 10mph, when it normally did (I've been on this hill many times in this car before), and I wasn't quick enough to gear down again, so I stalled. Fortunately, there was still a bit of distance with the car behind.
So I started the car again, and when I attempted going from 1st to 2nd, my car suddenly stalled, and when it started rolling back, the car behind was VERY close. I had to slam the brakes. Result: a chorus of beeping from the queue behind me!
When I got back on a level, I eventually realised there was a problem with second gear, when the car won't go past 5mph when in 2nd. I had to rev it up so much and go up to third gear.