Phi Day

Takes place 3 times annually, on the 6th of the month of January, on the 19th of the month of May and on the 31st of the month of October.

Hashtags:
References:
mathnexus.wwu.edu/archive/humor/detail.asp?ID=212
goldenratio.org/phi_day.html
mathjokes4mathyfolks.wordpress.com/2013/05/17/is-it-phi-day-yet/