rsl12 When commenting, remember that ALL comments must be polite, even when the performer has stated that any comments are allowed. If you need help making your criticisms polite, refer to <insert link to helpful document>. Thanks for helping to maintain a friendly environment!
I really liked WieWaldi's suggestion of "supportive" because you can also be polite and say "I humbly suggest you find yourself another hobby since it seems you don't have what it takes to play piano." Which technically polite, that's not very supportive. Again, this has not happened and I don't think we should expect it, but... you know. Humans. So how about
When commenting, remember that ALL comments must be polite and supportive, even when etc