[CoffeeLovesYou]

If you really want to do this (regardless of what Eosian said)
Go into your MEMBERINFO template
Find $vbphrase[edit_user_profile]
You should see

<if condition="$show['edit_profile']">
						<li class="thead"><a href="moderator.php?$session[sessionurl]do=useroptions&amp;u=$userinfo[userid]">$vbphrase[edit_user_profile]</a></li>
					</if>

Below that, add;

<li class="thead">$prepared[username]'s UserID: $prepared[userid]</li>

So it should now say;

<if condition="$show['edit_profile']">
						<li class="thead"><a href="moderator.php?$session[sessionurl]do=useroptions&amp;u=$userinfo[userid]">$vbphrase[edit_user_profile]</a></li>
					</if>
<li class="thead">$prepared[username]'s UserID: $prepared[userid]</li>

If you want it to just say UserID: # instead of My Hattiesburg's UserID: #, use this code.

<li class="thead">UserID: $prepared[userid]</li>

Enjoy.

(note: that's for VB3.8, not sure about the latest version, if you're using vB4, but it might still work)