a joke on the TV show friends
.....
RAch: Hey Joey, how'd the audition go?
JOey: Incredible, there's just one thing that might be kind of a problem. See, I, uh, had to kiss this guy. See, I'm up for this part of this guy, who the main guy kisses.
ROss: 【Well, hey. You're an actor, I say you just suck it up and you do it. (Rachel looks at him in disbelief) Or you just do it.】
....
My question is: why is everybody looking at Ross when he says "i say you suck it up and you do it?", is there anything wrong with this sentence? the audience is laughing like crazy. his girlfriend Rach is looking at him in disbelief as everybody else, so he deletes "suck it up" and just says "you just do it".

I may be paranoid, but i sense there's something dirty about 'suck it up', is it like "suck the other man's tongue up"? and make the kiss very passionate like a French kiss?

Question

a joke on the TV show friends
.....
RAch: Hey Joey, how'd the audition go?
JOey: Incredible, there's just one thing that might be kind of a problem. See, I, uh, had to kiss this guy. See, I'm up for this part of this guy, who the main guy kisses.
ROss: 【Well, hey. You're an actor, I say you just suck it up and you do it. (Rachel looks at him in disbelief) Or you just do it.】
....
My question is: why is everybody looking at Ross when he says "i say you suck it up and you do it?", is there anything wrong with this sentence? the audience is laughing like crazy. his girlfriend Rach is looking at him in disbelief as everybody else, so he deletes "suck it up" and just says "you just do it".

I may be paranoid, but i sense there's something dirty about 'suck it up', is it like "suck the other man's tongue up"? and make the kiss very passionate like a French kiss?

Answer

Yes, it is a bit vulgar but it refers to kissing having to do with sucking (tongues). A VERY vulgar expression describing kissing is "sucking face".
You are aware of the expression 'suck it up and do it' which has nothing to do with kissing.
So that's why it was a joke

Answer

I doubt that the writers intended any *particular* image of "sucking" to occur to the audience. Each person will conjure to mind some more or less humorous, but different, image associated with the word. It'll depend on the person. But it'll likely be enough to make us laugh--probably out of slight discomfort and embarrassment. The exactly origin of the idiom "to suck up" (meaning to endure a bad situation stoically) seems not to be clear. But it might be associated with taking a deep breath instead of complaining, or sucking in your stomach to appear tough.