Virtually Instant Maximum Guild Reputation (Patreon)

This morning I was completing the Alliance final 7th legion campaign with the quest "The Final Foothold" which is offered from Halford Wyrmbane in Borallus at level 118+. 

The quest requires you to click the table in front of Wyrmbane and select the final campaign-this will vary depending on what campaigns you have done. An automated quest completion windows pops up which if you click complete it awards you 125 guild reputation. This  quest is apparently different from the one Wyrmbane offers and is triggered by clicking on the table and selecting the final campaign. 

If you then abandon the Wyrmbane quest, accept it again, and keep completing the table quest, you will gain a lot of guild reputation very quickly. I don't know of any other way to max out guild reputation this fast, you can get exalted in minutes.

Be very careful not to accidentally click on Wyrmbane and complete his quest, you must only ever complete the auto-accept quest from the table. 

I have not yet tested this with Horde or with earlier stages of the campaign but I'm fairly certain the same mechanics apply: simply click on Wyrmbane or Nathanos Blightcaller (his horde equivalent), click on the table, complete the auto-complete quest, abandon, repeat.