When visiting a festival event that runs for a number of days (such as Glastonbury) a festibeard is grown through not shaving during said event. This can be as a simple function of ease considering inadequate access to bathroom facility or a test of manliness. In the case of the latter it's common to shave immediately before the festival to see how far the beard will grow over the allotted time scale.
"Oh man, I grew a massive festibeard but had to shave it off when I went back to work."
"You grew all that in just three days?! That's one fuck off festibeard!"