i'll start!
when i first started playing the game i only built the items that gave me the highest stats, no starting items even, just straight
boots of travel for speed
mjöllnir for attack speed
divine for dmg
and bloodstone for health, health regen, mana and mana regen
and by then the game was usually done cause i only played vs bots back when i did this. on a side note to this one, i also once used the bloodstone (which killed you at the time) and lost my rapier because i didn't know it dropped on death so it was just left on the ground and i had no clue what happened (reading tooltips is hard apparently)
i also have another one, i was playing my first game as pudge and accidently started rot(w), i didn't know i had to turn it off myself (maybe i tried but accidently clicked w an even amount of times, thus leaving it on, but i don't remember), this was back when it could kill him btw so yeah….. i didn't touch rot for the rest of the game.
Source: https://www.reddit.com/r/DotA2/comments/yvddkd/most_embarrassing_story_you_have_from_playing/