I heard about this technique a few months ago and mentally filed it it under “life hacks that probably don’t work”, but after I accidentally shrank my favorite sweater I decided to give it a try. Amazingly it works. Results may vary (polyester and wool un-shrink the most), but it does work.
Simply pour a tablespoon of hair conditioner into a bucket of lukewarm water and let your garments soak for half an hour. Dump the bucket, rinse the smelly water out, and then ring out your shirt and let it air dry. Bamf!