How do you describe calling someone a "Loser" when you mean it in a "good-natured" way

How do you describe calling someone a loser in a "nice" way? What word can replace "nice"?

There's a specific word I'm looking for but cannot dig it out of my brain.

"I mean loser in a   _____ way"

It's almost the opposite of "patronising" or "condescending".

Similar words but not quite right:

• good-natured
• friendly
• chummy
• affectionate
• sweet
• nice
• charming
• lovable

Context:

Someone calls me this word but I have known this person for a long time and know his humour and what he is like. He says the word often and with a great big smile on his face and arm over my shoulders. I find it funny/laugh when he says it. I am trying to describe this to another person who doesn't quite get it like I feel most people here don't!

Endearing is the best word for the sample sentence. (As the OP commented.)

Sample sentence:

"I mean loser in an endearing way."

Definition:

endearing (adj.) That endears: (a) that wins or inspires affection; (b) manifesting affection, caressing. (OED)

Not sure if that epithet can be sugar-coated though. It strikes me the same as those who would say:

"No offense but...you are a loser."

And, of course, offense is always taken.

Might as well say:

"I'm about to punch you in the nose but you aren't allowed to tear-up, okay?"

When I call you a "loser", it's only a bit of banter.

banter ˈbantə/.
noun.
1. the playful and friendly exchange of teasing remarks. "there was much good-natured banter".
— https://en.oxforddictionaries.com/definition/banter

And a second (Irish) one is:

When I call you a "loser", it's only a bit of slagging.

1.1Irish mass noun
Good-natured teasing.
‘there was a bit of slagging but it is all good craic’.
- https://en.oxforddictionaries.com/definition/slagging

Slagging of course has another definition - "An insulting and critical attack.", so depends on the audience if this one works.

One word for good-natured or light-hearted teasing is ribbing:

Cambridge Dictionary

informal the act of laughing at someone in a friendly way as a joke

YourDictionary.com

the act or an instance of teasing or ridiculing playfully

The word originates from "rib-tickling" or "poking someone in the ribs":

Dictionary.com

"tease, fool," 1930, apparently from rib (n.); perhaps as a figurative suggestion of poking someone in the ribs. Related: Ribbed ; ribbing.

YourDictionary.com

ribing; meaning 'teasing', from the common practice of tickling the ribs to cause laughter.