Regex match and replace for abbreviations

I think you want the following:

 "my friend u.c.l.a i c u. c that thing? u c that thing?".gsub!(/\bu(?!\.(?!\s))\b/i, 'you')

you regex pattern should look like this

    "my friend u.c.l.a i c u. c that thing? u c that thing?".gsub! /\bu(?!\.(?!\s))\b/i, "you";