Niceguy53 inserting a catheter without any lube would not cause any real injury, but it would be more uncomfortable as the lube allows it to glide up the urethra more easily. It may cause friction related trauma and considering the passage of urine , you may develop a UTI. UTI's in males are much harder to treat , often leading to hospitalization and acute renal failure . So I would think carefully about attempting a catheter without lube.
As for inserting with an erection , I have never encountered this in practice , so cannot really comment . As with any insertion of a Catheter please ensure strict asepsis ( to prevent UTI's) and ensure the person inserting it has experience. As I have seen trauma and hemorrhage from someone inserting a catheter and inflating the balloon in the urethra instead of the bladder.
In the UK we use instillagel when inserting a catheter.
Instillagel is a sterile gel containing a local anaesthetic and antiseptic which contains :
Lidocaine Hydrochloride (Local anaesthetic)
Chlorhexidine Gluconate Solution (Antiseptic)
Methyl Hydroxybenzoate (E218 (Antiseptic)
Propyl Hydroxybenzoate (E216) (Antiseptic)
in a gel made with Hydroxyethylcellulose, Propylene Glycol and Purified Water.