Girthmasterr Warns Matt Kalil 'Size Queens' Will Be on the Hunt

The big news about Matt Kalil's junk size has made him a marked man ... and "size queens" are on the hunt, or so we hear from a porn star who can relate.

Here's the deal ... Kalil, a former NFL-er, had his dong thrust into the spotlight recently when his ex-wife Haley Kalil said his size was just too much for her, likening it to at least a couple of Coke cans.

Porn star Girthmasterr tells TMZ … he can totally relate to Matt's story, since he found himself in the same situation more than a few times before his huge wang made him famous.

Matt has since remarried ... but Girthmasterr tells us that is not going to matter to "size queens" who are absolutely going to seek him out now.

GM has some advice for Matt, saying he could make millions in porn -- if his wife's cool with it! -- and says it would be wise to get a vasectomy ... because if the rumors are true, the dude is going to be in high demand.

On a more serious note … Girthmasterr says it’s important women feel comfortable with guys who're packin' -- and the essentials for well-endowed men include lots of lube ... and lots of communication in order to make each session a pleasant one.

We guess you could ask him himself this weekend, since Girthmasterr is in NYC for a pop-up (no pun intended) meet-and-greet for Brazzers.