I find this to be even worse when they are already on your nexus.
We got stomped soo hard that the enemy would taunt every time we showed on their screen, we got 2 afk (1 never connected and the other was lagging so hard he just gave up and quit), they get to our nexus....slowly and just start dancing and spamming emotes instead of ending. we had an open inhib my team kindly asked that they just "end it now" because there was nothing we could do to defend against them 3v5. we camped at our spawn waiting for them to take our nexus. and once they get our nexus low enough. they stop attacking and proceed to spam dance/taunt/emote to stall the game as long as possible while 3 of us were just sitting on our spawn doing nothing, they let the minions finish off our nexus but it took well over a full minute for them to do so while the enemy team proceeded to be total jerks about it..
Its like saying "GG Ez" without actually typing it out, and each and every time i leave the game very tilted and salty because of people like this, i find this behavior to be very very toxic. Its painful enough that we are powerless and can't even fight back and we **willingly give you our nexus ** so you can end quickly but you rub salt in our wounds by ignoring the nexus to make us feel bad?.
This has been happening in every single game i have lost, and lately i feel like this type of behavior has increased a lot.
TLRD; End our suffering by taking the nexus right away, don't sit there and stall out a game as long as possible in front of our open nexus just to make us feel worse for losing soo hard.