For me, what makes a forum boring or not is the quality of the posts. I don't come here to look at avatars. If it makes a big difference to you, you could set up your own style sheet for this site and increase the avatar size to any size you like. (I have my own user style sheet for this site, in which various elements are sized up or down to suit my taste. For example, I have the little gree icon next to the usernames of members who are online set to something much larger, so it's easier for me to see that they are online.)
It is a suggestion to take into consideration although I confess that I never had a problem with the size of the avatar itself.
Before asking, do a search... if you don't find the answer, then ask The purpose of this forum is to help others in the community, that's why it's called Sitepoint and not Linkpoint. SP Guidelines - No fluff.