Maybe a US/UK divide? At least in the UK boffin is relatively inoffensive depending on how it’s used. Eg if I build a fusion reactor in my garden my neighbour might say “wow, look at what this boffin did!” and it would be a complement where boffin is a stand in for a word like genius, only with a tounge in cheek touch of jealousy.

Thinking about it I would say that ‘nerd’ is typically putting someone down for their intelligence or interests, whereas boffin is a light insult while identifying the ‘boffin’ as being smarter than yourself.