I just came across this SO user whose username is
which spans more vertical space than "normal" characters when rendered on page, which looks ugly especially as a comment author, as seen here.
Should such characters be allowed in user names?
Also, if you see the comment, it's
O̷̼͓̤̣͕͍̠͍͝ͅͅM̵̶̛̙̟̫͇̪̖̯͕̩̝E͏̡̢̤͈̩͍̯̗͕͎͎̥̫̘̙͖͇̤̻͢͜ò̦̳͈̰̩̣̙͇̖̭̪̲͖̤͡͝ͅͅͅn̷͉̼̱͉͎̜̰͜_Ȩ̷̝̦͕̮̫͇͖̪̪̀͟͝ͅ ̶̱̳̼̝͖̹̹̻̣̺͓̜͜͞͡Ś̴̢̛̥̪̭̳̥̞̩̞̙̼͍̟̗̻̮͟A̵̛̮̪̗͎̺̼̯̠̘͉̼͠ͅi҉̩͔͖̳̰͕͉͕͓̘͚͙͔̰̦͔̜͘͝ͅd̥͔͖̥̠͎̻͍̣̯̞̗͇͜͜ ̕͞͏̰͕̠a̴̭̟̠̞̳͇̙͕̻̫̘̭͈̲̹̕͠ņ͉̣̻̩͜_ṇ̵̢̼̺͎͟ͅó̡҉̼̫̳͙̰͔ͅÝ̶̲̞͇̪͈̥̮̫̹͕͡Į̶̛͖͕͔̩͖̼_N̷̜̩̜̤̲̬̞̯͘͜G̟͍͔̹̣͈͢͡?̡̹̹̟͖̕͟͜͠
which also raises another closely-related question of whether such characters should be allowed in comments.
My opinion is "no" and "no", but such characters should probably be allowed in questions and answers, because they may be relevant/necessary.
However, if such characters are in Q/A posts just for "decorative effect", they should be edited away.