Not a full fail without explosions, but my recient Moho mission partially failed due to low TWR. Because of the insane dV requirements I decided to just send an ion powered spacecraft.
So, I get to Moho and guess what, the capture burn takes 5500 m/s and it takes over 2 hours! Wouldn't be too bad (have better timewarp mod installed), except there's a catch; the flyby only lasts for like 30 minutes. So I decided to give up and make it a flyby mission. Still allowed me to max the tech tree though
Also, a recient mission to the Mun almost failed because the lander tipped over. Instead of giving up though I used it as a rocket powered rover that crawled along the ground until I got to a nearby crater, then took off using the crater as a ramp