Well, let's see what's actually punishable, shall we? In my experience browsing the boards, I've seen punishments for:
- Consistent negativity
- Detrimental arguing
- Flaming
- Harassment
- Threats of violence
- Encouragements of self-harm
- Hate speech
- Trolling
- Intentionally feeding
- Non-participation
- Spamming chat
- Assisting the enemy team
And, while this looks like a fairly large list of things to get punished over, if you disregard the gameplay/zero-tolerance stuff (leaving harassment, flaming, detrimental arguing, consistent negativity, and chat spamming), that's five punishable offenses that are punished more on the basis of Consistency & Severity. Consistent, mild negativity (defeatism, report-rallying, for example) will ultimately earn the same punishment as inconsistent, egregious offenses (flaming, harassment), with different amounts of time for the punishment to arrive.
There's no golden percentage to look at for behavior if a player has recently been on a foul streak, they'll get punished. But one-off instances of negativity will not put you in the position to be punished.
Punishing people over anything else make you a petty child.
Well, hate to break it to you, but Riot will punish according to their rules, regardless of whether or not you view them as petty children for going against your subjective viewpoint.