In a bar, you may have noticed people banging their shot glasses on the table before they down their drink and thought "why are they doing that?"
Well, you're not alone. It's not entirely clear to some people why they are doing it either, and there are multiple explanations for the quirky custom.
One explanation is practical.
“It all dates back to the early juke joints, where sawdust was placed on the dance floor for easy cleaning should the necessity arise," bartender Sammy Mentkowski told The Drinks Business. “After particularly raucous wang dang doodles, sawdust particles would fill the air covering everything in the vicinity including the glassware. Tapping the glass on the bar was a way to remove sediment before taking a gulp of that sweet dancing juice.”
Now that we aren't knee-deep in sawdust like drunk hamsters, the tap is now used as a sign of respect to the bartender. However, there are other possible and slightly more morbid explanations, as highlighted by Mental Floss.
The practice may have evolved from "pouring one out" on the ground to remember a dead homie. The tradition is far older than you might expect. Known as a "libation", in Ancient Egypt people would pour water on the ground as an offering to the dead, or to a deity, and the same took place in Ancient Rome. The practice is also referenced in Genesis, with Jacob pouring a drink offering to God at the place where he had spoken to him.
One theory goes that tapping the glass is a newer, less-wasteful way of respecting the dead. It's a double respect bonus if the deceased also happened to hate spillage.
In Ireland, meanwhile, it was apparently a superstition that tapping the glass dispels spirits (the Casper kind, rather than rum).
It's fair to say these ancient meanings are lost on many people doing shots today, but perhaps that's ok. The bartender feels respected, your dead friend feels remembered and you, unaware of all this, get to bang your glass on the table (fun) and then drink a shot.
[H/T: Mental Floss]