They don't replace things they use, and get sullen when called out. They avoid making any firm commitments or get mad when asked to, and will agree to things they won't do instead of speaking up to say just that.
Too big or busy to respond to calls for chores, they stay disconnected from general maintenance routines around the house. Their angry verbal/physical reactions when issues are raised make you dread engaging, and overlook instead.
Who can easily go months late on rent without talking about it, rack up debts without tracking or payback? You guessed right, your flatmate from hell. Quite needy in times of lack, but surprisingly selfish in times of plenty? Does this ring a bell?
Now I've known good and bad flatmates, but once I ran into this other type. Zero contribution most times, but 100% entitlement to an equal share. Prayed in loud voices and spoke in tongues, but went 6 months without speaking to folks who were subsidizing his rent. Funny, when conflicts happened he would still be the first one to yell.
Did he move out after finding his feet to give his hosts some needed space? Of course not. A classic poor communicator, even basics like "discuss move out plans without prompting" and "leave as stated", got complicated. The dates dragged months, then into and over a year so it was quite in character when his confirmed move out date finally came by to spot him still at the apartment,without a word to anyone saying why.
Remarkably, these types always approach as the original term runs out to say "Hey, let's move in together again"
AND GO THROUGH ALL THIS AGAIN?
See, these flatmates are never self-aware enough to understand that anyone who's lived through hell, would never want a part 2.