I have to say, university was a disappointment to me for similar reasons. I naively expected to arrive in a place where people liked to think, learn and discuss ideas. First thing I saw was a truck advertising cheap lager, with Top 40 hits blaring out of two huge speakers. This set the tone for the next three years. It wasn't until I started my MA that I met people who would admit they enjoyed thinking.
I mainly stave off brainrot by reading non-fiction, particularly science writing. The sciences are good from that perspective, because new and challenging ideas are always coming along even while I'm learning about established and obselete ones.
I do have a few smart friends, but most of them I rarely get to talk to. Annoyingly enough, it seems to be easier for me to get into other people's special interests than for them to get into mine, so I end up mainly listening. It's also a problem that I get stressed out by long conversations- I have a friend who, when he visits, will happily talk for five hours straight about everything under the sun. It's all fascinating stuff, but my head stops coping after a while.
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You're so vain
I bet you think this sig is about you