ok ok ok wait hold on....
alright, so i see where you're coming from. there are many times when you shouldn't be doing things too seriously. like when i play a friendly match with someone and we're both laughing and having a good time, i just find it plain disrespectful if... say i were falco, and i just do something like Fthrow someone of the edge -> forward smash their double jump -> spike them. that's just ********, and it doesn't make it fun for my opponent, or if he were to do the same against me, i'd just be like... man, it's just not fun playing against you
instead, when i play friendlies with someone, i always try to do a bunch of different things to make everything more fun. for instance... if i was pikachu on FD, and my opponent was fox, i wouldn't just chainthrow them to death, or just Uthrow -> Usmash all the time, i'd try to do something like Uthrow -> Dsmash -> tech chase into a Dtilt -> run behind them and pivot grab, etc etc
or... let's say i'm grabbing the edge against a falco, i know that i could just roll back on the edge and they'll die, but instead i'd try something like ledgehop Uair and land on the stage, turn around, and shorthop Tailspike him, then dropzone Dair his Up-b
just a bunch of random stuff that you probably wouldn't do in a tournament match. this just makes things a lot more enjoyable and fun for everybody. the opponent should react in the same way, and just do a bunch of silly stuff, you know what i mean?
but i don't think you should have rules, such as "no killing your opponent downwards". there shouldn't be "rules" in friendlies, but there are many things that can take away respect from a player
In my position as a pikachu main, no killing downwards would be just stupid, because then that would take away tailspiking, which is a huge part of pika's game
friendlies should just be about doing fun and new things. for instance...
as falco, you could just jump out and Dair your opponent, then double jump -> up-b back onto the stage
but in a friendly, for things to be more fun, you should probably do something like jump out, Dair your opponent, then Dair him a second time for a Suicide kill
ok so maybe that wasn't the best example, but...
basically, there are times when you should play seriously, and there are times when you should just be silly and stuff
if you're at a tourney with a bunch of people that you might not ever see again for a long time, i feel that most "friendlies" you play with someone else, you should probably treat it as a tournament match. when you play with new people, it's generally a test of skill. you don't practice so much just to show someone how silly you can be. you should show someone new the level of skill you have, so both of you have an understanding of who might be the better player. i'm not saying that you should camp the crap out of someone that you just meet in a friendly, but i'm also not saying that you should sandbag to an extreme. i feel that you should just try hard enough to get an understanding of each other's skill
however, if you're playing someone for a long period of time... i feel that you should start out with seriouslies, then gradually continue on to being just friendlies
there are times, however, where you can play someone for a long period of time and have the entire time be serious matches.
alright, in short... don't set restrictions on what a friendly should or should not be. if you don't like playing with the person that you're playing with, i recommend to find another person to smash with. in your situation, if someone thinks that they're better than you, show them that they're not if that's what you truely think. maybe challenge them in a money match. or if you want to play a serious match, just tell them. tell them to try their hardest for a few matches and you'll do the same for a test of skill. then after you guys decide who's better, continue on to friendlies