How the heck am I supposed to wish them a happy birthday??

According to http://knowyourmeme.com/memes/sites/imgflip
Imgflip was created on June 14th 2008 by Dylan Wenzlau (the guy in the picture) and on that date had 2 registered users and 13 hosted images. Therefore, Imgflip's 10th birthday will be June 14th this year.

Indeed

Thanks!
But also who's Watson?

Dr. John Watson - Sherlock Holmes's partner. Good-natured, brave, and down-to-earth, Watson is Sherlock Holmes's sidekick, even though he rarely helps Holmes actually solve any mysteries

Oh okay.

Cool

Now I know when to create happy birthday memes for imgflip, xie xie so much!

Some users had been onsite for up to four years before Raydog joined.

just search the oldest imgflip acount i got anonymous as the oldest at 2012

imgflip tech support

Here is the site registration info, looks like June 29, 2011 but I'm no authority on the subject:

Domain Name: IMGFLIP.COM
Registry Domain ID: 1664319968_DOMAIN_COM-VRSN
Registrar WHOIS Server: whois.tucows.com
Registrar URL: http://tucowsdomains.com
Updated Date: 2017-06-14T23:05:04Z
Creation Date: 2011-06-29T03:14:48Z

All the fun I've had here over the past three years

Just guess it, like how I do it with my friends.