you blame your loss in the fact your opponent had a "Good atch", or a "Nice combo" etc.
...or perhaps you had a close match that you thought was fun and you were... I dunno...
telling them that?
I don't freaking tell someone gg if I play badly and lose. I also don't freaking tell someone gg if they clearly made a huge mistake that cost them the match. A "good game" is by definition (imo), a close, fun match, regardless of the outcome.
If they combo'd you, and you couldn't get out of it, saying "nice combo" is an acknowledgement of their skill. It's not an excuse as to why you lost. Saying "If it weren't for that combo of yours, I could've won," or "I DIed really bad on that..." on the other hand, now that's making an excuse out of it.
Complimenting your opponent doesn't have anything to do with johning. In fact, acknowledging your opponent's skill is the exact opposite of a john. A john is an excuse as to why you lost; you think you should've won for some reason, and you are
refusing to acknowledge your opponent's skill.