Beetlejuicing is when oneuser posts a comment or thread on reddit, and another user with a username relevant to that parent comment or thread responds.
It is not beetlejuicing if the commenter does not respond "naturally." Summoning someone with /u/ or asking them a question about their username is not beetlejuicing.
an over-the-pants handjob in a public place, often associated with patrons of musical theater
The congresswoman from my district got caught Beetlejuicing her boyfriend at the local theater, but she had to finish him off in the car because they got thrown out.
A term coined by the band blur used to describe people who smoke heroin, particularly those addicted to the practice. The term comes from the dotted black residue left behind on tin foil sheets after use, often called "beetles", hence the phrase "chasing the beetle".