No question about it... They have a higher chance to flame and blame then random people wich sometimes doesnt give a shit.
I was trying to duoQ and honestly its the worst experience of my life... After a winning streak 5 games or so where i had to carry my "duoQ" partner he started flaming everyone on the team for being bad when we was losing... for some reason he also started flaming me for not doing the calls he made or if i said "No" to baron when they had 1 second or was respawning (simply because thats the most common throw).
Me and this fella went from silver 5 and to silver 4 and 3 then after we lost I stopped duoQing (mostly because mmr sites wouldnt record my progress because of duoQ... haha yeah)... But also because he was getting more and more toxic... Now he is silver 5 and i am silver 3 and hopefully climbing.
(this guy even went AFK in one of my ranked matches, tho we won 4v5)... main reason i stopped duoQ as well.
But this is not the only reason i say this tho...
In most chases where i get duoQers in my team... I lose.. I dont know why, but 80% of the time i get duoQers in my team... They lose hard and they flame hard. I have had multiple instances where people have gotten worse from drawing first blood to going 1/10 because duoq'ers are flaming and blaming people for being "bad"
And it totally make sense that duoQ partners would be more toxic, because they are like "omg easy match, they have troll pick teemo" "So ezy elo" and when it doesnt go like that, they go "omg we troll"
Chances are you will even get matched with higher "ELO" players because you get duoQ partner.
DuoQ partners arent always hard to carry... But they can sometimes make it impossible to carry by feeding multiple lanes, and when their lane go to shit, they feed other and even your lane because "they simply dont give a F anymore"....
I will say tho that i certainly have had good premades too... they are just very very very rare in some chases they are neutral too.. :)