There have been a few specific people over time that have been notorious for causing this, mostly from repeated association of the person with things like fear, nervousness, inferiority, and rejection. Only one remains, thankfully, and even so I don't always have the burst of anxious shock anymore (a feeling like all my insides vanish for an instant, and may include light-headedness, which is what 'butterflies' are to me), though I do still feel like a wary little rabbit thereafter. The rest I either have shed that reaction to over time or they've just gone away themselves.
Other things that can cause 'butterflies' like crowds and going someplace new without any familiar people to 'shield' me, though that depends a lot on the degree of crowdedness or distance out of my comfort zone, as well as my mental state at the time and whether I'm fed/rested and stuff like that.