I think "insultar" is a little strong for "slight". At least, there is
an important distinction in English between insulting someone and
slighting them. The dictionary says:
1. To treat as of small importance; make light of.
2. To treat with discourteous reserve or inattention.
a. To treat with gross insensitivity, insolence, or contemptuous
v. tr. [LC] Ofendre amb actes o paraules ultratjosos [ultratge: Injúria
greu de fet o de paraula].
Perhaps "no tenir en compte" would be closer. For example, I might
slight someone without meaning to, by not taking them into
consideration or by ignoring their opinions or feelings. Generally
speaking, I don't think you can insult someone inadvertently.
All the best (Adéu-siau),
Potser podem posar "desairar" o "menystenir".