I know that if a user is removed, all his votes will be cancelled. So some users may have negative reputation changes as a multiple of 10 or 5. But How -2 reputation change for user removal? I got this message few minuets before. Any idea?
The rep change reported for removed users is the total effect. You don't know how many actions are involved in that. So if you've been reasonably active yourself -- have lots of posts that could be voted on, have accepted answers, have edited, etc -- then just about any number is possible. No breakdown is available.
Maybe he downvoted 4 your posts and upvoted one of your answers. Then in total he gave you 2 reps. When he is removed, these two reps are removed. Only one event shown, summed up of all votes the removed user casted on your posts.
Most probably you suggested an edit on a post and received 2 reps. The user (and his/her question) was removed, thus the 2 points you gained were taken back.