Is it normal to sniff your boyfriend's armpits?
Mostly.Normal for most people
Yes—being drawn to your partner’s natural scent, including their armpits, is a pretty normal quirk. If you both find it funny or enjoyable, there’s no problem with it.
Lots of people find a partner’s natural smell comforting or attractive, even when it’s a bit sweaty. Smell is tied up with familiarity and attraction, so your nose may simply be a fan of your boyfriend.
As long as he’s comfortable with it and you’re not making him feel self-conscious, sniff away. If he’s not into it, let the armpits have their privacy.