Come to think of it, yes I have. In the early 90s I won a competition on a box of cereal or something, and the prize was a Townsend Aardvark.
Picture shamelessly stolen from... this very forum!
In the early 90s I was considerably too small to ride a full size bike. So my mother wrote to them and they sent a child's bike, and this one was put in the garage... until 2006 when I went to uni in York. It was my trusty steed on approximately one journey, and spent the rest of the year chained to a railing outside my accommodation. I would occasionally use it to play 'bike-tennis' and it ended up in the lake more than once. We always fished it out, though.
At some point I lent it to a friend-of-a-friend, but by the time of graduation he hadn't returned it, and I was convinced I'd never see it again. Well, actually, I'd forgotten about it.
Until one day I came home from work (I had changed courses and worked in a bike shop for 18 months or so to raise funds) and I saw it in the front garden! Apparently the friend-of-a-friend had given it to his friend with the instructions to return it to my house when he no longer needed it!
It was in a bad way. Both mechs were seized up and the rear wheel was pringled. I rebuilt the brakes, found a new wheel in a skip, and converted it into a singlespeed, and used it as a hack for about six months when the BB crumbled into nothing.
I tried to give it to a bike recycling charity but they weren't interested. Oh well, I left it in the city centre... two weeks later, and it was still there. Then, one day, it was gone. Finally!
Eventually I moved away from York (*sniff*). I hired a van to move my stuff but it was significantly cheaper to return the van to York and catch the train home than it was to do a one-way journey in the van... so, back up to York, locked up my house for the last time. I was walking to the station along the river and saw a bike lying in a wooded area... a closer look, and it was that bloody bike again! So, I rode it to the station (it really was unrideable by this point), left it unlocked, got the train and never saw it again... for now!
That's my story about the world's worst bike.