What's the scariest thing happen to you on a bike (not involving a driver)?

I've fallen on ice once (bike just shot off sideways as I came out of a junction turning left).

Most embarrassing fall was trying to get out of the way of a bus coming out of my village and I thought, "I'll go up that dropped kerb there onto the pavement for a spell".

Unfortunately catching my wheel in a worn section of tarmac just before said dropped kerb, and the kerb wasn't as dropped as it ought to have been: the bike went over, I came off, did a roll onto my back and lay there laughing at my own stupidity as the bus and its passengers all went slowly past...

I've gone on ice once. The night before had been -5 but I kept to the main roads as surely they had been gritted. Got to close to work where I had to take a right at some lights (lucky for me it was a green right filter so oncoming traffic would have to be stopped). I just noticed a couple of vehicles were stopped on the other carriageway withj their drivers having a "fender bender" chat as | approached. Just as I wondered if that meant there was some ice the front wheel went on the turn and me and the bike slid all across the carriageway coming to a half just in front of the stopped cars. I got up and moved myself and the bike out the way as the lights changed. Yep, no one asked if I was ok. 
I checked the council website when i got into work. Turned out they hadn't sent the gritters out as they didn't think the temperature was too low.  

I also went over on slippery bricks along a canal recently as well. Wasn't doing more then 8-10mph. A lady walking her dog suddenly appeared at a bridge. I braked to stop to let them through, and a combination of paniers loading, camber and disc brake forces sent the suddenly slightly locked back wheel right. My bike ended up facing the other direction on the floor. 

Rendel Harris wrote:

Not sure if it counts as the scariest thing to happen, as not much actually happened, but riding up a long climb in the Alpes Maritimes and hearing, seemingly pretty close by, the howl of a wolf was probably the most scared I've been on a bike, probably the fastest I've climbed for many a year as well! (It sounded as if it was coming from down the mountain, so turning back didn't really feel like an option)

Similar thing happened to me, but with a twist.  I was climbing the Blockhaus in Abruzzo, on a section just after a village.  The road zig zagged up the mountain, and there was a shepherd and his 4 dogs taking the straight route, so they seemed to be crossing the road at the same time as I was labouring up the climb, which happened about 4 times.  The dogs look a bit like large retrievers, but they can be vicious.  They're bred to deal with wolves! 

Not only that, the shepherd was wearing red speedos, which really freaked me out...

What a beauty, though I certainly wouldn't want to be on its wrong side! That's interesting actually because I was relating my story to a guy in a bike shop in Nice and he said that I was lucky it was a wolf and not wild dogs, because apparently the wild dogs in that region are absolutely fearless and will attack anything whereas the wolves are quite solitary and tend to shy away from human contact. Wish I'd known that at the time!

keeping it dog related, and light hearted,  I was cycling home one night from work in the winter, and using a short section of cycle path thats badly illuminated, so it was dark, misty, damp and there was no-one around I could see.

and as I approached a section of overgrown bush on my side, this huge black dog suddenly leapt out of the bush at me, and my bike light picked up its eyes, so all I saw was a huge black dog with teeth bared growling and with glowing eyes jumping towards me at handlebar height, I thought I was seeing Black Shuck (local folklore legend hellhound/hound of the baskervilles type thing) brought to life.

no idea how I stayed upright or didnt hit the dog, it was just then the owner walked round the corner on their mobile phone, as I had probably yelped quite loudly in fright, and they muttered some form of apology. took a while for my heart rate to recover.

Thanks for sharing. This road was frequented regularly by friends and myself when we were kids and we attacked it with youthful fearlessness and never any incidents. I dare say we were never as fast as we envisaged, but still recall the joy it brought.

Similar sort of thing for me, a dip in a road I usually rode in the other direction, suddenly the bike gathered speed and got away from me; I couldn't make the curve at the bottom and I crashed into a wire fence, writing off my front wheel. 

Not as scary but had similar incidents as well with SPD two bolt. Hadn't been an issue on one bike as the clip tension was less, but had gone on the "shopping bike" and just got to the supermarket and realised the shoe was not unclipping. Cycled home, took the foot out of the shoe and turned the shoe until the cleat jammed against the tread and has leverage to unclip. 

Also had something similar when an overlarge overshoe wedged between the cleat and the clip and I didn't realise until I stopped at lights and couldn't unclip. Unfortunately I had already leaned that way but luckily was close to the pavement as the plan was to rest my foot on the kerb. So fell flat down. However as I couldn't unclip, and the left leg was under the bike, getting back up again was very tricky.