Grandma Found Grinder

Just picked my grandma up from her cruise which she went on with two gay men.

Me: How was your holiday grandma? 
Grandma: Well very interesting. Do you know what gay men can do now on their phone? 
Me: Uh...? 
Grandma: Chris showed me. It's this thing called Grinder. 
Me: He showed you Grinder? 
Grandma: Yes. Just the picture on it. Not his face. 
Me: oh