I usually get ragequits on WiFi when I do any of the following
- Nayru's Love on Mega Man Fsmash, any powerful charged neutral B, or on Villager's Tree
- spamming Nayru's Love in general when I notice my opponent won't punish it
- sweetspotted dair -> fair/bair on stage
- Elevator
- cutting off a recovery with uair
- any 2 stock that ends with a dair
Most people don't ragequit on me I feel. I often end up against players that I am clearly better than who will just keep playing me. I just finished 90 minutes against a Sheik who wasn't able to win at all, but they did get better, so I guess they enjoyed it. If I go against someone who beats me a few times and then gets 2-stocked though, it's a guaranteed quit.
The above is almost always from a Little Mac, a Shulk, a Link, or a Rosalina.