I don't own a torque wrench so I am completely ham fisted, I also grease everything (not any more, I use copper slip, assembly paste and grease) so these are a mixture.
Rounded all the bolts off on a ritchey stem, the heads are made of cheese, I swear. Ive got round it by not greasing the bars.
Snapped carbon seat post. (being ham fisted)
BB30 cranks fell off because I didnt have the spanner to tighten the preload so did it by hand, it did not work.
Didnt check if my tyre was seated proceeded to pump them up to 60psi before they furiously unseated and spread sealant evenly all over the garage.
edit: extra bonus, filled a clutch master cylinder with 15W40 for a project at work, all the seals swelled and it no longer moves, no leaking though..