Today it's cypto-currencies like Bitcoin. In 2000 it was technology shares. In 1987 it was shares in general, and way back in the seventeenth century investors were going nuts over tulip bulbs.
When it comes to investment, fads occur when asset prices are driven up by irrational excitement, greed, and 'FOMO' - the fear of missing out. The fundamental rules of valuing an investment fly out the window and speculation dominates trading as hoards get caught up in the frenzy before experiencing a crash.
While it may be difficult to resist the temptation to join in I would, instead, put my money only into investments that I understand; those with values based on more realistic capability of generating long-term income and/or capital growth. I wouldn't rule out the occasional small flutter on a 'speckie', but it would come out of my entertainment bduget rather than being part of my core portfolio.