Creepers in a small cave you come accross while digging down and you think you can explore it a bit because there's some iron and coal but it starts getting complicated and you do what you can to keep a wall at your back but IT-IS-IMPOSSIBLE: they always end up blasting your bottom xD
Creepers. For some reason I never have a bow on me, and it seems like no matter many torches I have up, they still manage to sneak up on me. My front yard looks like a WWI minefield.