When I lived in Florida as a teenager, I was roaming around a wooded area (central Florida, Putnam County) and came across a small cactus around a foot or two high. I was curious what the inside of it was like and it didn't have very big spines to it, rather it was easy to grab it and avoid the spikes, however when I used my knife to cut the top off, I was met with very neatly aligned needles filling it. They were yellowish but clear and there were millions within the plant in neat rows lining the whole inside. Within seconds my whole body was coated in them and I quickly dropped the piece in my hand and ran home where I stripped and did everything I could to get the needles out of my skin and out of my clothes, but I ultimately had to throw away my clothes and seek help to get rid of the ones embedded in my skin. I have searched off and on since this only to find that cacti should be hollow or simply green inside. I am curious what this plant is, as I have had a severe fear of cacti since and fear that a cactus fruit is simply made of the same thing and will just fill my mouth with thousands of needles if I attempt to try it. I want to know if anyone can tell me what this plant was so that I can hopefully get over my fear but it looked like a small cactus.

Opuntia with some sort of insect infestation?? I dont really know

@Baja_Costero does this sound like something you've seen before?

I'm wondering if it was an Opuntia, which can look smooth and thornless but can still have virtually invisible little glochids all over it, and the irritation you felt was from touching the outside of the cactus?

Or could you have also touched some this in the process? Just touching a flower can cause misery:
Stinging Nettle (Cnidoscolus stimulosus)

This is interesting. I have never heard of a cactus like this. I suspect it may be something else, not a cactus, but I don't really know.

I was completely unaffected touching the outside of the plant, I was able to grip it and give it a short look over before I cut off the top and that was when I noticed the inside just looked like it was made of millions of neatly stacked/lined up yellowish needle like things that I thought were fibers until I realized a split second later that they were embedding into my skin. I think some had gone airborne when I pulled the top bit away from the plant after cutting it. It definitely looked like some sort of succulent and now that you've given me a name I do not recognize, I am going to look and see if maybe that is what it was!

So it definitely wasn't stinging nettles, I saw those everywhere in Florida and avoided them like the plague after stepping on one. However, this Opuntia thing you guys pointed out looks extremely similar to what I cut, except the one I cut was very very small, maybe only a foot or two tall. I do not know if maybe they have a defense at that size where they are filled with needles to keep things from eating it but that is my only conclusion so far is that maybe it was an extremely young cacti or succulent with a defense system.

That is horrifyingly fascinating! I'm sure somebody will come by who recognize what you're describing.