There is this friend I have which has always been a little “different” (no negative connotation) and with which I recently reconnected and started spending more time with. And even though I try to be tolerant and mindful of others difference, there are plenty of annoying factors there for which mental illness as an explanation would make sense.

They constantly boast about their IQ or ingenuity or their above-average skills and attempt to mask it with it being poorly subtle. Sometimes they just start talking about it out of nowhere. This also connects to their constant search for new hobbies and almost immediate declaration of their brilliance. They’ve been into various sports, philosophy, psychology, magic, rhetoric and many more. They’re okay at them for a beginner, but they claim that they have potential to be great (before abandoning the interest a week or so in). 

They also seem to lie a lot, mostly about very big things (which are either false or blown out of proportion) like confronting people, fighting, “owning” someone in an argument and other absurdities. It also seems like they talk about their mental state a lot, claiming having everything from aspergers to adhd to depression to schizophrenia to not being mentally ill. 

They have, in general, close to no humility and are full of arrogance, but then have bouts of apparent self-loathing and despair which, at least to me and friends around, seems clearly fake and just an attempt to gain attention.

Although this is hard to withstand (and my description has a slight ring of animosity to it) they are, more than anything, still my friend and I see something going on which is very bad for their mental health and even for those around them. What is wrong with them? How can I / we help?