When people are first timing a champion they often dont mention it soon, instead mention it very late in the game. And i wouldnt believe them because to me it sounds like an excuse for them feeding. Seriously just mention it in the lobby so were aware that youre not gonna be very good.
I avoid mentioning it at all. It has the potential to tilt teammates or start an argument, and doesn't seem to have any real upside.
I've seen some instances where someone did announce they were going to first-time a Champion in the pre-game lobby, and as soon as it was said, someone dodged. (albeit it was fairly rare, and it hasn't happened for quite a long time, so, there's that).
Besides that outlying risk, there's a number of factors to consider about whether or not someone does announce they're first-timing:
These are just a few that pop into my mind, but even then, this is just abstract math that probably doesn't go through anyone's mind - let alone those who actually are first-timing a given Champion.
I imagine, the only thing going through someone's mind when they first-time is something along the lines of "this Champion looks cool, let's try them out" - and they say nothing about it to anyone. And that first half can be changed out for other stuff - "maybe I should branch out into Jungle with this Champ," "Oh hey, I just got a skin for this Champ", "I just got this Champ" - etc.
In the end, it really shouldn't matter if someone's first-timing a given Champion. Some may use it as an excuse, others may joke, and some will be sincere, and some may not even bother to tell you - but in the end, whether or not they're first-timing shouldn't really have an impact on how you play*.
*With some exceptions, of course - if they're first-timing an ADC and you happen to be their Support, a little flexibility goes a long way.
I assume you're talking about normal games ? I mean it's normal to expect that people are trying new champions this way, not a lot of people are playing normal with mastery 7 it's kinda pointless.
The very idea that people use "first time" as an excuse honestly bothers me a lot.
First of all, we all have bad games no matter how many times we've played a champion.
Secondly, you being unfamiliar with a champion's mechanics, doesn't (or shouldn't) hinder your common sense to not dive the enemy 1v3 or not use your wards when they're available. Being new to a champion doesn't explain away poor decision making... it only explains why you might not be the most mechanically proficient... have low cs, etc etc.
