So recently I was trying to signup for an account on Instagram but to my surprise I got a message saying I already had an account with Instagram. If I ever signed up for an account it must have been a long time ago since I didn't have the creds on my LastPass or any traces of emails sent by Instagram to my email account.

In any case I then tried to reset the password in my unknown existing account when to my second surprise I got this message back:

That was really frustrating since I thought I wasn't going to be able to use my email with Instagram for some technical issue that made my account to get locked and unreachable.
After googling for a bit and getting nowhere I suddenly recollected, probably from an old Security Now podcast, the mention that Steve Gibson made that you could add a + to a gmail address and google would still be able to reach your account.

If that was possible, then technically I would be able to register another account on Instagram using a different email handler but pointing to my actual gmail account.
I found this post in the Gmail blog describing in more details

Append a plus ("+") sign and any combination of words or numbers after your email address. For example, if your name was hikingfan@gmail.com, you could send mail to hikingfan+friends@gmail.com or hikingfan+mailinglists@gmail.com.

Insert one or several dots (".") anywhere in your email address. Gmail doesn't recognize periods as characters in addresses -- we just ignore them. For example, you could tell people your address was hikingfan@gmail.com, hiking.fan@gmail.com or hi.kin.g.fan@gmail.com. (We understand that there has been some confusion about this in the past, but to settle it once and for all, you can indeed receive mail at all the variations with dots.)  

I put that to a test and as expected I was able to register an account on Instagram with the email diogogmt+instagram@gmail.com

Now, the funny part is that I've been giving my email for years as diogo.gmt@gmail.com even though the actual email is just diogogmt@gmail.com