OMG, I searched methylene blue because I saw it as possible sensitizer for alternative photography. But WTF! It looks like I landed on a chemical misinformation landmine. Everything on YouTube about this chemical sounds like bullshit. This link looks very bullshitty but as I listening to it, this may be one of few links that have some information on this stuff.
Use its red counterpart on an already red drink if you want to give someone old a scare