Riot make this a warning if not report option

This is a rare situation for me but riot should make it a warning for all new players that they should be somewhat experienced with at least some of the roles and champions. I once played with someone who was last pick and claimed that he could ONLY play Vayne adc. Assuming this guy was telling the truth, that meant that he would have to hope to be lucky enough to get adc AND that vayne wouldn't be banned or picked by the enemy team, since vayne is a popular champion. If he could play one or two other roles, that would be fine, but ONLY Vayne adc? That's ridiculous. I didn't report this guy, but I hope he learned his lesson. I told him to play team builder because it supports what he wants, a way to play ONLY one lane and ONLY one champion. He could either ONLY play vayne adc or practice another role and champion of his choice. Please try to make this happen riot.