@alh …bingo! That’s it…I should be concerned at this point, with parenting my son. What I find uncomfortable, what others may perceive of him, her and any others he may have. If her family is comfortable in thei home with that behavior, then what can I say? But he needs to know there are many, many more that are more reserved, and different variations of that also. Hand holding, great. Pecking…alright, Whatever. Lap sitting, full fledged kissing. No. And if he dates someone else, he better be careful. I’ll remind him of his grandfather. 
OP: Is there any indication that they are doing these five second kisses in anybody else’s homes but the homes of their parents, where she, at least, must think it must be comfortable to do so? And first you said these kisses/lapsitting lasts five seconds; now you’re saying she lays all over him. Which is it?
“I do have a high bar for gf/bf interaction”
What does this mean, OP? According to you, the girl is 20 and your son is 21. They’re still in the learning process, yes?
I’m sorry, but this particular OP seems like she is having a hard time letting go of her sons. (Someone asked her upthread in the first sentence if she had daughters and OP did not answer. Based on previous posts, she does not have daughters.) In particular, she wrote about how unhappy she was that her sons did not acknowledge her birthday the way she wanted in a long, recent thread. One called her from college and the younger one told her happy birthday. But she wanted a (non-store bought) gift and some “effort”, especially since they spend money on themselves and their girlfriends. (18 pages, that thread!)
Two Sons and No Birthday Gift: http://talk.collegeconfidential.com/parent-cafe/1708603-two-sons-and-no-birthday-gift.html#latest
After discussion here, she ended up writing them an email. When other posters asked her - multiple times - what response she got from her sons, she never answered though she continued to post on other subjects. The last post in that thread is "What ever happened, conmama? "
In other words, this is a mom who is having a hard time not being #1 in her sons’ life and they are not toeing her line. Which is perfectly normal, but she’s couching it as if it’s the girls they date who are at fault for whatever. (Also perfectly normal but not acceptable). I’m guessing any good, real advice she gets here is not going to be heeded until she works on the underlying issue.