Stock expert Jim Cramer has cautioned that the market is at its most overbought, sparking debate about his tweet being an April Fools' joke. Meanwhile, signs of market overbought conditions in U.S. index-based exchange-traded funds are noted. Despite reaching all-time highs, the S&P 500 index remains on a bullish streak, and the relationship between Bitcoin and stock market indices is explored. Additionally, BlackRock sees Bitcoin as a strong portfolio diversifier.