Onling gaming term for "team killer" or "team killing". Used verbally as well as in typing. The act of killing your own teammate rather than the enemy.

Noun: a friend who is usually only called upon by a friend when a more primary/prominent friend is unavailable.

Taken from the term “second string” in an athletic competition situation. In football, if the star quarterback gets injured during a play, the second string is called off the bench to replace him/her. A “Second String Friend” is essentially benched until needed, if ever.

Synonyms: Plan B, Second Choice, Secondary Friend, Benched Until Needed

In the Professional Printing Industry, TK on a work order means "to come".

Team Killer n.
A person who engages in intentionally or unintentionally killing teammates in online games. TKs are either unskilled or are trying to ruin the gaming experience for others. The latter can be summed up by the Battlefield 1942 term smacktard.

A babyface south philly legendary villain, that makes Nick Foles look like an itsy bitsy jalapeño in the locker room. Full sleeve tattoos galore inked up to include a picture of the “S” brothers on each butt cheek. Craves amazon binge shopping, hole munching, and assassinating each putter he grips. Truly, the most generous and kindest person you will ever meet.

When somone makes a joke, but then it's carried on beyond beleif; to the extent that it's fully and utterly killed.
somone is then at liberty to call a 'TK', and the job is done.

Anything that is messed up, strange, dumb, or absurd.