frenemesis 

A person with whom you have a long-standing or close relationship, but who is the ultimate frenemy. An arch-rival who pretends to be your good friend, while undermining you behind your back.

She's not just a frenemy, she's my frenemesis.

frenemesis by nodramamama November 11, 2010

Fremesis 

The one person (or thing) in your life who gives you an endless supply of reasons to hate them but who you inexplicably cannot imagine life without. An even more vehement title than frenemy. Could be used to describe the relationship between Magneto and Professor X.

Hard-boiled, lonely detective: "Damn you, liquor. You've ruined my marriage and chased off everyone close to me, but you make life worth living. I love you, my fremesis."

Fremesis by DrunkandDisorderly October 3, 2012

Friemesis 

A friend who is also a nemesis. More than just a frienemy, a friemesis is an archrival.

A friemesis is your worst frienemy.

Friemesis by paters November 10, 2010

frenemesister

That female at work that is sometimes friendly, sometimes your nemesis, sometimes you want to strangle in a sibling kind of way.

That damn frenemesister - yesterday she brought in brownies and today she's in my office talking about office style & credenzas - I don't know whether to strangle, hug, or defenstrate her.

frenemesister by PabloNachos82 January 22, 2021

frienemisis 

a close friend that is also your greatest competition. you strive to out do, undermine and defeat eachother at every opportunity, while still maintaing what appears to be a close friendship. whether you are actually friends depends on how you truly feel...

keep your friends close, your enemies closer and your frienemisis closest

frienemisis by PLB March 27, 2012