Can u get banned for saying bannable things in the lobby with your friends?

What do you mean by "lobby" - the pre-queue lobby/party lobby, or the pre-game lobby/Champion Select?

If it's the former, then, no, I've not seen any cases where someone was punished for party lobby chat.

If the latter, then, yes, it's possible to get banned for misbehavior in Champion Select.

If you're in a 3-/5-/6-man premade, you generally should be certain that your friends won't report you, but if you do get reported, your behavior would be reviewed, and rulebreaks in pre-game and post-game lobby will be held against you.

EDIT: Although the meaning is generally implied by the premade-size, it'd probably be good for me to clarify anyway, that the premade team sizes are listed for respective gamemodes;

3-man premade being the max for Twisted Treeline (Normal, Ranked, Co-op VS. AI), 5-man being the max for Summoner's Rift (Co-op VS. AI, Normal, Ranked, RGMQ), and 6-man being the max for Twisted Treeline (RGMQ - Hexakill).

If you're not in a full premade team, your behavior will always run the risk of a report by anyone outside your premade, so, bear that in mind.

If someone reports you, yes. The system can access pre- and post-game chat.

Your best bet is too keep toxic/negative chatter with your friends in Discord and PMs.

Thanks for the replies! I meant in the lobby with friends before the que even begins! I was just curious about it with my friends so i decided to ask here! Thanks again.

Any report will trigger the system so if a angry player on opp team reports you out of spite if you said things that are bannable you will be punished, even if the player on the opp team didn’t see that chat so be careful and probably don’t use that kind of language in lol chat.