Portmanteau of 'sick' and 'pervert'.
Same meaning as 'pervert', one who practices sexual perversion. However, where 'pervert' is already often stigmatised, 'sickvert' connotes an added judgment value of repulsiveness, beyond simple quirkiness.
Also a verb.
"Johnny likes to rape mentally and physically disabled people. He is a sickvert."
"I thought we'd just have good old perverted fun together, but he turned out to be a total sickvert! I'm never seeing that freak again."
"Billy used to be a fun kinky boy, but now Bobby has completely sickverted him."
"Paul seemed like a sweet guy, and then Jimmy found out Paul had been stalking him, taking pictures, and obsessing over him. What do you know, Paul was in fact a sickvert."