I stepped on a thumbtack

[Alyx Vance]

I was bike riding once and brushed up against a thorn tree, cut my arm in 8 places. I now have 8 scars on my right arm.

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[SWAT One]

Once I stubbed all of the toes on my right foot, lept up in surprise,  and then stomped on a thumbtack with my left.

[Pah1023]

I once stepped on a cactus, those tiny needles are a pain.

[Insomniac]

My brother put a thumbtack in the hallway once and as I was walking I ended up stepping on it. That motherforgeter got stuck in my heel, extracting it was quite painful.