feeding for IP during party bonus weekend?

so, there's something that i've seen advertised a lot around reddit. people join a chat room and bring 5 people into a game for party IP bonuses, and then run down mid twice and afk.

this makes it so that the enemy team can end REALLY quickly. and since you're in a party of 5, you get a ton of IP even for a loss. ip farming.

is this legal? i personally have no problems with it, i haven't done it, but as someone that's been playing for 4 years and still needs to spend a ton of IP on champs, runes, and rune pages.. i can understand why people would do it and i don't hold it against them.

i've been told that it's not bannable as long as your entire team agrees to it, but i've also been told that if the enemy team gets pissed off about having an easy 10 minute win (for some reason, oversensitive children) they can report you and you will be permabanned

if someone with a reliable source can tell me whether or not this is allowed that would be great, seeing as i actually need a ton of ip still. i would do it but i don't want my main banned.