The art of wiping the top of your ass crack with the backside of your thumb and smelling it.

A jack off buddy (from 'cum' /'come', meaning 'semen', and 'companion'); a friend that you get together with for sessions of solo or mutual masturbation
Variant of: cumpanion (from 'companion' & 'cum'); jack off buddy & wank bud & JO buddy
Similar to: fuck buddy

Generally used as an insult to someone who is not funny at all and boring to the point of you wanting to physically harming them.

The word "craic " is an irish word that is used in the north of england and also scotland for the banter and fun and enjoyment people have with eachother. Adding "top" to this and changing craic to a more simpler crack gives it a more ironic use " topcrack".