We only know my mom’s maternal grandparents for sure, because they came from Germany in 1903. I’m 1/4 German.
The other 3 lines (mom’s paternal grandparents, dad’s grandparents) have been in America too long (over 150 years) to have any good idea. What we think (in order of supposed amount): English, Irish, Native American (based on 1 photo), German, and maybe French. With 3 English surnames for those 3 lines, it’s pretty certain English is the most predominant.
Dad: French/Irish
Mom: German/Irish
I was born and raised in Britain, but both parents are from western India.
As far as I know (as always, a high probablity that there is something else in the mix somewhere ;)):
Maternal:
Grandmother:
Scots-Irish, perhaps a smidge of German
Grandfather:
French, perhaps also Irish/Scots-Irish 
(Not much info on his family, but hers was here for ages)
Paternal:
Grandfather:
Scottish
Grandmother:
English
(both immigrants from the UK, my father was a 1st generation American)
I was born in El Salvador. I know very little about how my relatives came to the country but my mom tells me her grandpa was from Spain. He had a cool ass name too: Santana Villareal. On my dad’s side there’s at least a dude from Sweden that came over in the early 1900s. My gramma on my mom’s side is native indian though.
On my mother’s side: Scottish, Welsh and German.
On my father’s side: Heinz 57. Irish, German, English, French (from a family whose members fought on different sides during the 30 Years War), Dutch, Welsh, Swedish and Montauk Indian. (The Montauk woman married a Dutch ancestor in the 1650’s, shortly before smallpox killed 2/3 of her tribe.)
French-Canadian.
As were both parent.
Dad’s side: English, German (via Switzerland,) Italian
Mom’s side: English (via United Empire Loyalists,) Welsh, German (via the Pennsylvania Dutch)
Swiss isn’t an ethnicity of its own, is it? As I understand it, you have Swiss who are ethnically German, ethnically French, ethnically Italian and so on. If not, then I’m Swiss on my Dad’s side, along with the others.
Canadian-American. We have probably 40 or 50 ethnic festivals in my hometown, but none for this particular one.
Going a bit further back, it’s English, Scots, (northern) Irish, Welsh, German, Flemish, Dutch, and probably even more WASPy stuff I don’t know about. My great-great grandfather Squire was made a ship’s captain on the condition that he leave England and never return. An annoying lot, we are.
Weirdly enough, there’s no Scandinavian. But in my early 20s I was a dead ringer for Benny Andersson (of ABBA), to the point where my own mother mixed up the photos. And every year I see a whole stadium full of people with my exact hair when I watch the Dag Nyheter Galan track meet from Stockholm.
Canadian, White (although the Government says I’m “Indian”).
Blue eyes, brown hair (blonde when a child).
Paternal Grandfather - Irish and Scots.
Paternal Grandmother (Maiden name: Meyers) - German, but she would describe it as “Pennsylvania Dutch”.
Maternal Grandfather - Scots on his father’s side, Ojibwa and French on his mother’s side…
Maternal Grandmother (Maiden name: Tudrick) - “Ukrainian”, but we’re not exactly sure – likely Slavic of some sort for sure, may be White Russian. Apparently she claimed that when she was a little girl (somewhere between 1875-80) there was a war going on and they could hear the cannonfire as they fled from their home. I never knew her, so I can only go on what my mother had to say about it.
Irish
Irish
And so on, way way back. Cannot rule out a Viking or an Englishman somewhere along the line.
1/16 Swiss (my great-great-grandfather being from near St. Gallen)
3/16 German
3/4 Irish (with some Scottish and English thrown in)
American Mutt - 99% various European/British/Irish/Scots, 1/64th Native American.
My mother is 100% Polish
My father is 50% Polish and 50% Bohemian (on his mother’s side)
My grandfather used to call us kids “Bohacks” (lBohemian-Polacks) to annoy my grandmother. On both sides, it was my great-grandparents who came over to America.
As far as I can remember I’m:
Mostly:
Scot
Irish
Minimally:
English
French
Jewish (some really small %, but I like to toss it in.)
I know my grandmother could rattle off the litany of our ancestor’s lineage, and it’s way longer than I have there, but I can’t remember all of it. I’m a mutt with Celtic influences. Both sets of great grandparents came over from Europe. One side via Canada (I think he was a lumberjack for a while) and I don’t know how the other set got here.