Oh my where do I start here? There's a number of situations I could list, so let's start with one that will annoy me for all time. I was on a North East Rover, which I barely used and that was bad enough. Time wasn't on my side with the couple of days off from a labouring job I had tried at the time, and let's just say I'd not recommend that to anyone, so I did what I could with one of the most expensive tickets I've ever bought. It was a Bank Holiday weekend from memory in 2007, and there were London to Leeds trains diverted over the curve at Hambleton West Junction. To get to it, I was travelling west from Brough after having to alight from the HST there due to late-running which would mean missing the train to Doncaster I'd needed to be on. I never did get Brough to Hull for HST coverage, and that also annoys me.
Anyway, a 185 rolls in and I was quite pleased with that as I recall 185s were limited to Hull at the time. Something about weight restrictions on that line? It's 16 years later, I honestly can't remember for sure! Foolishly, I'd forgot the Northern service a bit later than the 185 is what I wanted to be on, and I bailed at Selby so I could get to the B&B I'd got booked in York. When I got there, the owner had fallen asleep waiting for me to arrive as it was, I dread to think what he'd have thought of me if I'd arrived on the revised itinerary I'd been given to do that track. To this day, I've still got that curve at Hambleton West to do and I just don't know if I'll ever get it done. When I discovered I'd got on the wrong train, oh boy that was embarrassing. I spent a *lot* of time on the railway in the mid-2000s, so I should have known better!
There's been two charter trains I've fallen asleep on as well, one along the Weardale Railway and once on a Class 40 charter on the Far North Line. In fairness, I'd stayed up all night on the overnight charter, it was bound to happen! Back then, June 2007 I believe this was, I wasn't drinking coffee regularly and I have no idea how I survived! Fortunately I'd been awake for the bulk of the charter, so it wasn't too bad but still a bit on the embarrassing side!
I'm sure
@Kite159 will remind me if I don't mention it, but in more recent years I got my 'ford' stations mixed up. This was well before 321s were being withdrawn, so I don't know when it was, but it was in the last 6 years. By now, I'd been travelling on trains for too many years to make stupid mistakes. I'd run over to join a winning 321 at Liverpool Street, off another train, and saw what looked like Stratford on the screen. Good, not a first stop Shenfield, cool beans. Straight through Stratford, oh maybe I was wrong. Shenfield, non-stop too. Eh? What? This service was non-stop London to Wickford in the morning contra-peak! I'd mis-read Wickford as Stratford, oops! Thankfully they sorted me out in the ticket office and I got back to London firmly with my proverbial tail between my legs!
I have others where I fell asleep and didn't wake up when I expected to, ensuring a change of plan to the day. It happened once on an overnight 185, in 2011, from Manchester Airport, and I'd planned to alight at Huddersfield to do the line towards Barnsley. I woke up just after the doors had locked! Thankfully I was on an ALR so could change my plans and I ended up on a XC HST from Leeds to Sheffield, from where I picked up a solo 153 (that sounds odd in the current era!) on a Saturday special towards Cleethorpes. I did eventually get the line from Huddersfield to Barnsley done, memory doesn't tell me when though.
Another time I remember way too fondly for unknown reasons, this would be back in 2004 from memory. I'd done an all-nighter in Manchester, no not in the pubs/clubs! To be honest, now I've typed that I'm amazed I never did such a thing. Anyway, I was on the 0527 or something like that out of Manchester Piccadilly and I was going via Birmingham New Street on the way back to Swansea. Unsurprisingly I'd fallen asleep and I woke up just before Birmingham International. I was so embarrassed I went and bought a single back to Birmingham, joining a full and standing Voyager the one stop. My next move to Cardiff was a 170, and unsurprisingly I fell asleep again during the journey. Somewhere I woke up and thought I was on the bridge into Newport, so I got up and ready to alight. I then saw I was passing through Chepstow! Nowhere near my destination of course, so at least I didn't miss my next train, but that was a bit awkward as I must have looked like a right pillock!
I have many other situations where I look back and wonder what lunacy was going on, but I'll not go into those. 19 years have passed since one of those not-to-be-discussed moments, I still haven't forgot that time in front of 3 or 4 RPIs! Or the group meet with some other enthusiasts in 2007 at Nuneaton where one of the group pretended to be diving in front of a passing train! One last situation I'll discuss though, and yes this is one where I look back and wonder what grade of idiot I was at the time. No I don't want an opinion on that

This was in the mid 2000s, again, and yes I did spend way too much time on trains back then! This was a period when FGW HSTs were diverted between Cardiff Central and Bridgend via Barry, and I had my head out of the droplight. Somewhere along the line was some vegetation that slapped me across the face and I've not forgot that! I've also remembered the time I high-fived someone on a passing train at Bristol Parkway, now that was beyond stupid and outside the scope of this thread!
I didn't think I'd had as many embarrassing moments, and no I haven't got to all of them! I guess it's been the best part of 2 decades, there's bound to be a lot!