PSA; "Wanna duo?"
(Before I get in to this, has anybody been asked "wanna duo" by someone higher ranked than them? Diamond friends never ask, but gold and silvers are hitting me up every day until I tell them to piss off >_>)
So, you want to duo in Ranked with a friend you met in-game (normals, ranked, bots, what have you), do you? Alright! There are a few (three) steps you need to take before you ask someone to duo, or if they want to duo with you.
Step 1 - Check their rank It stands to reason that a fair many higher-elo players will not want to duo ranked, especially not with lower-ranked players (talking whole Leagues below). It's a handicap and Ranked is for tryharding. It's generally seen as "Will you boost me" if a lower-ranked player asks someone to duo, ESPECIALLY if they haven't played any games with you recently. If they're an IRL friend, or you've done Ranked together a lot and they just ranked faster than you did, this isn't applicable because irls tend to play together a lot.
Step 2 - Check their badge Y'know that thing Riot has implemented, with the solo-dynamic-team badge after 25 games? That isn't only visible to the person who has the badge! It's a simple few clicks to pull up their profile and see if they have a Dynamic/Team badge. If you see a Solo Preference badge, odds are the response will always be a "no", as solo is their preference, and they've played at least 23-24 out of the past 25 games in solo queue.
Step 3 - Chat them up first Nobody, and I mean nobody, likes seeing something like this; "Hey wanna duo?" with no chat history or communication. That is another outlying cry of "Hey please boost me". If you talk to them frequently and get along, invite them for a few normals, and then on your next Ranked spree invite them along.
Disclaimer: This thread was made out of frustration at "wanna duo" messages out of nowhere. Rules are dynamic and may differ from person to person. Stop playing Teemo in Ranked and asking people to duo. I'm looking at you, Sharon.