Here's my first attempt at a Riley! Good luck!
Sit down, relax, or sleep for a while.
One point six times five point eight, then less three.
Which definitely is not a song.
Rest is a synonym for relax, etc. and people look forward to it wistfully, with smiles on their faces.
Tau (twice pi) is approximately $6.28$, which is $1.6 * 5.8 - 3$. Clued in by @Omega Krypton.
Rest - which means to relax and is pleasing for many people.
Rant - A lengthy, angry impassioned speech.
Infix 1.6*5.8-3=6.28, which is 2*pi, so infix="pipi"
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